Sputtering target, oxide semiconductor film and semiconductor device

ABSTRACT

A sputtering target including an oxide sintered body, the oxide sintered body containing indium (In) and at least one element selected from gadolinium (Gd), dysprosium (Dy), holmium (Ho), erbium (Er) and ytterbium (Yb), and the oxide sintered body substantially being of a bixbyite structure.

TECHNICAL FIELD

The invention relates to a sputtering target and an oxide semiconductorfilm. The invention relates to a semiconductor device, in particular, toa semiconductor device using as a semiconductor crystalline indium oxidehaving a prescribed electron carrier concentration.

BACKGROUND ART

An oxide semiconductor film composed of a metal composite oxide has ahigh degree of mobility and excellent visible light transmission, and isused as a switching element, a driving circuit element or the like for aliquid crystal display, a thin film electroluminescence display, anelectrophoresis display, a moving powder display, etc.

As the oxide semiconductor film composed of such a metal compositeoxide, a zinc oxide-based crystalline thin film (Patent Document 1) hasattracted attention. However, zinc oxide has a defect that it lacksstability, and hence, a very few of them were put into practical use.

Non-patent Document 1 discloses a thin film transistor using anamorphous transparent semiconductor film composed of indium oxide,gallium oxide and zinc oxide. However, since this transparentsemiconductor film is amorphous, it has poor stability.

In addition, the above-mentioned indium oxide contains a lot of oxygendeficiencies in its crystal, and therefore, is used as a transparentmaterial improved in conductivity. However, when indium oxide is used asa material of an oxide semiconductor film, the amount of oxygendeficiency cannot be controlled. As a result, indium oxide becomes aconductive material, making the use thereof as a semiconductor of anoxide semiconductor film difficult.

The above-mentioned oxide semiconductor film composed of a metalcomposite oxide has further disadvantages that the field effect mobilityis as low as 8 cm²/V·sec or less and the on-off ratio of the current issmall. In addition, a sputtering target used in producing theabove-mentioned oxide semiconductor film has poor conductivity, andhence, a DC sputtering method, which is industrially advantageous,cannot be used, and hence, only a RF sputtering method can be used inproducing the above-mentioned oxide semiconductor film. For thesereasons, these oxide semiconductor films are not suited to practicaluse.

Furthermore, an active matrix-type image display apparatus such as a LCD(liquid crystal display) and an organic EL (Electro Luminescence)display has been widely used in view of display performance, energysaving or the like. In particular, it has come to almost constitute themainstream as displays of cellular phones, PDAs (Personal DigitalAssistant) and personal computers, laptop computers and TVs. Generally,a TFT (field-effect type thin film transistor) substrate is used inthese displays.

For example, a liquid crystal display has a configuration in which adisplay material such as liquid crystal is filled between a TFTsubstrate and an opposing substrate, and a voltage is selectivelyapplied to this display material for each pixel. Here, a TFT substratemeans a substrate on which a TFT using a semiconductor thin film (alsoreferred to as a semiconductor film) such as an amorphous silicon thinfilm or a polycrystalline silicon thin film is arranged as an activelayer. The above-mentioned image display apparatus is driven by theactive matrix circuit of a TFT. Since a TFT is arranged in the shape ofan array, a TFT substrate is also referred to as a “TFT arraysubstrate”.

Meanwhile, in a TFT substrate used for a liquid crystal display or thelike, a set of a TFT and one pixel of the screen of a liquid crystaldisplay (this set is referred to as one unit) are arrangedlongitudinally and laterally on a glass substrate. In a TFT substrate,for example, a gate wire is arranged longitudinally at equal intervalson a glass substrate and a source wire or a drain wire are arrangedlaterally at equal intervals. In addition, a gate electrode, a sourceelectrode, and a drain electrode are respectively formed in theabove-mentioned unit which constitutes each pixel.

A transistor using the above-mentioned silicon thin film is produced byusing a silane-based gas, and hence, it is disadvantageous in respect ofsafety or equipment cost. In addition, an amorphous silicon thin filmhas an electron mobility which is as low as about 0.5 cm²/V·s when usedin a TFT. In addition, since an amorphous silicon thin film has a smallband gap, it may absorb visible rays to cause malfunction. Moreover, apolycrystalline silicon thin film requires a heating process which isconducted at relatively high temperatures, needs a large amount ofenergy cost, and it is hard to be formed directly on a large-sized glasssubstrate.

Under such circumstances, a TFT using an oxide semiconductor thin filmin which a film can be formed at low temperatures has been activelydeveloped. With the development of the above-mentioned TFT, asemiconductor device or the like using an oxide semiconductor thin filmhas also been developed. Further, in order to obtain a flat paneldisplay (FPD) which is thinner, lighter in weight and higher inresistance to breakage, an attempt has been made to use a resinsubstrate or the like which is light in weight and flexible instead of aglass substrate.

For example, Patent Document 2 discloses a technology of a thin filmtransistor using an oxide semiconductor film composed mainly of zincoxide which can be formed at low temperatures.

In addition, Patent Document 3 discloses a technology of a field effecttransistor using as an active layer (channel layer) an amorphous oxidecontaining at least one of In, Zn and Sn.

However, the thin film transistor in Patent Document 2 is required to beimproved in transparency or electric properties as a transistor or thelike.

In addition, since the transparent semiconductor film used in thechannel layer is amorphous, the field effect transistor of PatentDocument 3 has problems that the characteristics thereof may changelargely with time or by heat, or the threshold voltage may changegreatly when used for a long period of time. In particular, in theproduction process, if a heat of 300° C. or higher is applied, forexample, thermal changes in the characteristics thereof has become agreat obstacle for industrialization. One of the reasons is that thenumber of careers is too large or that the film is amorphous. Anotherreason is that the move of oxygen tends to occur easily and the carrierconcentration tends to change easily since oxygen is forced to beincluded in order to increase the partial oxygen pressure at the time offilm forming.

In addition, it is difficult to control an amorphous transparentsemiconductor thin film, since a large amount of oxygen tends to beintroduced at the time of film formation. As a result, the carrierconcentration tends to change with the passage of time or byenvironmental temperatures. For this reason, it is necessary to controlaccurately the oxygen partial pressure at the time of film formation.Therefore, an amorphous transparent semiconductor film is defective inreproducibility, stability or the like for industrialization.

Furthermore, since this transparent semiconductor membrane is amorphous,its resistance to chemicals such as an etching solution, therepresentative example of which is PAN, is low, a metal wiring on thesemiconductor film cannot be subjected to wet etching. Moreover, it hasa defect that the refractive index is large and light transmittance of amultilayer film is lowered easily. In addition, since this transparentsemiconductor thin film is amorphous, it may adsorb oxygen, water, orthe like in an atmospheric gas, whereby electrical properties of thefilm may be changed and thus the yield may be lowered.

That is, an amorphous oxide has a problem that control of electroncareer density is difficult, and hence it is poor in stability,uniformity, reproducibility, heat resistance and durability.

Patent Document 1: JP-A-2004-273614

Patent Document 2: JP-A-2003-298062

Patent Document 3: JP-A-2006-173580

Non-Patent Document 1: NATURE, vol. 432, p488-492, (2004)

An object of the invention is to provide a sputtering target which canbe crystallized at relatively low temperatures and is capable ofproducing an oxide semiconductor film having stable semiconductorproperties.

Another object of the invention is to provide a sputtering target whichis improved in conductivity and can form a film by using a DC sputteringmethod.

The invention has been made in view of the above-mentioned problems, andis aimed at providing a semiconductor device improved in transparency,electric properties, stability, uniformity, reproducibility, heatresistance, durability or the like.

DISCLOSURE OF THE INVENTION

The inventors made studies on an indium oxide-gallium oxide-zinc oxide(IGZO) semiconductor, and as a result, the inventors have found that,generally, IGZO forms a stable amorphous phase. Further, since most ofthe IGZO compositions show an amorphous phase, an IGZO semiconductordoes not show stable semiconductor properties at high temperatures.

In the case of indium oxide alone, oxygen deficiency may tend to occureasily. As a result, a large number of carrier electrons generate, whichmakes it difficult to render the electron conductivity small. Therefore,when no transistor gate voltage is applied, a large amount of currenttends to be flown between a source terminal and a drain terminal, and aTFT cannot realize a normally-off operation. In addition, it appearsthat increasing an on-off ratio is also difficult.

Furthermore, when indium oxide with an electron carrier concentration of10¹⁸/cm³ or more is used in a channel layer of a TFT, a sufficientlylarge on-off ratio cannot be attained. Accordingly, it is not suited toa normally-off TFT.

That is, in conventional crystalline oxide indium films, it wasimpossible to obtain a film with an electron carrier concentration ofless than 10¹⁸/cm³.

The inventors prepared a TFT in which crystalline indium oxide with anelectron carrier concentration of less than 10¹⁸/cm³ is used as anactive layer of a field-effect transistor. The inventors have found thata TFT with desired properties could be obtained, which can be applied toan image display apparatus such as a light-emitting apparatus.

Further, the inventors made intensive and extensive studies oncrystalline oxide indium containing at least one of Zn, Mg, Ni, Co andCu or crystalline oxide indium containing B, Al, Ga, Sc, Y and alanthanoid element, and film-forming conditions of this material. As aresult, the inventors have found that, by containing at least one of Zn,Mg, Ni, Co and Cu, or by containing at least one of B, Al, Ga, Sc, Y anda lanthanoid element, the electron carrier concentration of crystallineoxide indium can be less than 10¹⁸/cm³.

In order to attain the above-mentioned object, the semiconductor deviceaccording to the second aspect of the invention is a semiconductordevice in which a crystalline oxide containing indium is used as asemiconductor, and the crystalline oxide has an electron carrierconcentration of less than 10¹⁸/cm³.

As mentioned above, by using as a semiconductor a crystalline oxidewhich has properties superior to those of an amorphous oxide, it ispossible to improve stability, uniformity, reproducibility, heatresistance, durability or the like of a semiconductor device. Inaddition, when a semiconductor device is a field-effect transistor suchas a TFT, it is possible to provide a transistor improved intransparency, electric characteristics, large-area-uniformity,reproducibility or the like. Here, the semiconductor device meanssemiconductor elements, semiconductor components, semiconductorapparatuses, integrated circuits or the like.

It is preferred that the above-mentioned crystalline oxide be anondegenerate semiconductor.

In this way, it is possible to reduce an on-off current and to increasean on-off ratio.

The nondegenerate semiconductor means a semiconductor which showsnondegenerated conduction. Here, the nondegenerate conduction means astate in which thermal activation energy in the temperature dependenceof electrical resistance is 30 meV or more.

It is preferred that the crystalline oxide contain a positive divalentelement.

Presence of a positive divalent element has an effect of extinguishingcarriers generated by oxygen deficiency, whereby the electron carrierconcentration can be decreased.

In addition, although being smaller than the electron mobility of asingle crystal, the electron mobility of a thin film formed of acrystalline oxide can be large.

Further, in the case of a thin film composed of a crystalline oxide,oxygen is fixed more stably. In addition, it has a high field-effectmobility, and the composition range for a stable crystalline oxide canbe expanded.

It is further preferred that the positive divalent element be at leastone element of Zn, Mg, Ni, Co and Cu.

In this way, indium is solid-solution-substituted by at least part of apositive divalent element such as zinc, whereby the electron carrierconcentration can be effectively suppressed.

Further, it is preferred that an atomic ratio of the number of the atomsof the positive divalent element ([M2]) to the number of the atoms oftotal metal elements contained the crystalline oxide ([A]) is0.001≦[M2]/[A]<0.2.

With this range, it is possible to obtain a more stable crystallineoxide. In addition, the electron carrier concentration can be controlledto be less than 10¹⁸/cm³.

Further, it is preferred that, by at least varying the atomic ratio of[M2] to [A], the electron mobility to the electron carrier concentrationof the crystalline oxide logarithmically proportionally increase.

In this way, semiconductor properties can be set easily, and the addedvalue of a semiconductor can be improved.

It is also preferred that the crystalline oxide contain a positivetrivalent element other than the above-mentioned indium.

Presence of the positive trivalent element has an effect of suppressinggeneration of oxygen deficiency. In addition, by using a positivedivalent element and a positive trivalent element simultaneously,carrier generation can be suppressed further effectively.

In addition, although being smaller than the electron mobility of asingle crystal, the electron mobility of a thin film formed of acrystalline oxide can be large.

Further, in the case of a thin film composed of a crystalline oxide,oxygen is fixed more stably. In addition, it has a high field-effectmobility, and the composition range for a stable crystalline oxide canbe expanded.

It is also preferred that the positive trivalent element be at least oneelement of B, Al, Ga, Sc, Y and a lanthanoid element.

In this way, the crystalline oxide can be effectively stabilized due tostrong ion binding properties of B, Al, Ga, Sc, Y and a lanthanoidelement.

As examples of a lanthanoid element, La, Nd, Sm, Eu, Gd, Dy, Ho, Er, Tm,Yb, Lu or the like can be given.

It is preferred that an atomic ratio of the number of the atoms of thepositive trivalent element ([M3]) to the number of the atoms of totalmetal elements contained the crystalline oxide ([A]) is0.001≦[M3]/[A]<0.2.

With this range, it is possible to obtain a very stable crystallineoxide. In addition, the electron carrier concentration can be controlledto less than 10¹⁸/cm³.

Further, it is preferred that, by at least varying the atomic ratio of[M3] to [A], the electron mobility to the electron carrier concentrationlogarithmically proportionally increase.

In this way, semiconductor properties can be set easily, and the addedvalue of a semiconductor can be improved.

Further, it is preferred that the crystalline oxide have resistance toPAN.

In this way, the degree of freedom in the production process isimproved, whereby the semiconductor device can be produced efficiently.

It is preferred that the concentration of Li and Na in the crystallineoxide be 1,000 ppm or less.

In this way, the properties change only slightly even when driven for along period of time, whereby the reliability of the transistor can beimproved.

It is preferred that the crystalline oxide be used as a channel layer ina field-effect transistor.

In this way, the stability, uniformity, reproducibility, heatresistance, durability or the like of a field-effect transistor can beimproved.

The invention has been made in view of the above-mentioned problem. Ithas been found that a sputtering target which contains indium, and atleast one element selected from gadolinium, dysprosium, holmium, erbiumand ytterbium is capable of producing an oxide semiconductor film whichis crystallized at relatively low temperatures and suffers from a slightdegree of oxygen deficiency, whereby the invention has been completed.

The invention provides the following semiconductor device, sputteringtarget and oxide semiconductor film.

1. A sputtering target formed of an oxide sintered body,

the oxide sintered body comprising indium (In) and at least one elementselected from gadolinium (Gd), dysprosium (Dy), holmium (Ho), erbium(Er) and ytterbium (Yb), and

the oxide sintered body substantially being of a bixbyite structure.

2. The sputtering target according to 1, wherein an atomic ratiorepresented by M/(In+M) is 0.01 to 0.25, wherein M is the content ofgadolinium (Gd), dysprosium (Dy), holmium (Ho), erbium (Er) andytterbium (Yb).3. The sputtering target according to 1 or 2, wherein the sputteringtarget further comprises a positive divalent metal element and thecontent of the positive divalent metal element to the total amount ofmetal elements contained in the sputtering target is 1 to 10 at %.4. The sputtering target according to 3, wherein the positive divalentmetal element is zinc (Zn) and/or magnesium (Mg).5. The sputtering target according to any one of 1 to 4, wherein thesputtering target further comprises a metal element with an atomicvalency of positive tetravalency or higher, wherein the content of themetal element with an atomic valency of positive tetravalency or higherto the total metal elements contained in the sputtering target is 100ppm to 2000 ppm in atomic ratio.6. The sputtering target according to 5, wherein the metal element withan atomic valency of positive tetravalecy or higher metal element is atleast one element selected from germanium (Ge), titanium (Ti), zirconium(Zr), niobium (Nb) and cerium (Ce).7. An oxide semiconductor film comprising indium (In) and at least oneelement selected from gadolinium (Gd), dysprosium (Dy), holmium (Ho),erbium (Er) and ytterbium (Yb), and the oxide semiconductor filmsubstantially being of a bixbyite structure.8. The oxide semiconductor film according to 7, wherein an atomic ratiorepresented by M/(In +M) is 0.01 to 0.25, wherein M is the content ofgadolinium (Gd), dysprosium (Dy), holmium (Ho), erbium (Er) andytterbium (Yb).9. The oxide semiconductor film according to 7 or 8, wherein the oxidesemiconductor film further comprises a positive divalent metal element,wherein the content of the positive divalent metal element to the totalmetal elements contained in the oxide semiconductor film is 1 to 10 at%.10. The oxide semiconductor film according to 9, wherein the positivedivalent metal element is zinc (Zn) and/or magnesium (Mg).11. The oxide semiconductor film according to any one of 7 to 10,wherein the oxide semiconductor film further comprises a metal elementwith an atomic valency of positive tetravalency or higher, and thecontent of the metal element with an atomic valency of tetravalency orhigher to the total metal elements contained in the oxide semiconductorfilm is 100 ppm to 2000 ppm in atomic ratio.12. The oxide semiconductor film according to 11, wherein the metal withan atomic valency of positive tetravalency or higher is at least oneelement selected from germanium (Ge), titanium (Ti), zirconium (Zr),niobium (Nb) and cerium (Ce).13. A semiconductor device using a crystalline oxide comprising indiumas a semiconductor, wherein the crystalline oxide has an electron careerconcentration of less than 10¹⁸/cm³.14. The semiconductor device according to 13, wherein the crystallineoxide is a nondegenerate semiconductor.15. The semiconductor device according to 13 or 14, wherein thecrystalline oxide comprises a positive divalent element.16. The semiconductor device according to 15, wherein the positivedivalent element is at least one element of Zn, Mg, Ni, Co and Cu.17. The semiconductor device according to 15 or 16, wherein the atomicratio of the number of the atoms of the positive divalent element ([M2])to the number of the atoms of total metal elements contained in thecrystalline oxide ([A]) is 0.001 [M2]/[A]<0.2.18. The semiconductor device according to 17, wherein the electronmobility to the electron carrier concentration of the crystalline oxidelogarithmically proportionally increases by at least changing the atomicratio of [M2] to [A].19. The semiconductor device according to any one of 13 to 18, whereinthe crystalline oxide comprises a positive trivalent element other thanindium.20. The semiconductor device according to 19, wherein the positivetrivalent element is at least one element of B, Al, Ga, Sc, Y and alanthanoid element.21. The semiconductor device according to 19 or 20, wherein the atomicratio of the number of the atoms of the positive trivalent element([M3]) to the number of the atoms of total metal elements contained inthe crystalline oxide ([A]) is 0.001 [M3]/[A]<0.2.22. The semiconductor device according to 21, wherein the electronmobility to the electron carrier concentration of the crystalline oxidelogarithmically proportionally increases by at least changing the atomicratio of [M3] to [A].23. The semiconductor device according to any one of 13 to 22, whereinthe crystalline oxide has a PAN resistance.24. The semiconductor device according to any one of 13 to 23, whereinthe concentration of Li and Na contained in the crystalline oxide is1000 ppm or less.25. The semiconductor device according to any one of 13 to 24, whereinthe crystalline oxide is used as a channel layer in a field-effecttransistor.

According to the invention, it is possible to provide a sputteringtarget capable of producing an oxide semiconductor film which can becrystallized at relatively low temperatures and has stable semiconductorproperties.

According to the invention, it is possible to provide a sputteringtarget which is improved in conductivity and is capable of forming afilm by a DC sputtering method.

According to the invention, it is possible to provide a semiconductordevice improved in transparency, electrical properties, stability,uniformity, reproducibility, heat resistance, durability or the like byusing a crystalline oxide having properties which are more improved ascompared with an amorphous oxide.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 is a schematic cross-sectional view of essential parts of afield-effect thin film transistor which is a semiconductor deviceaccording to one embodiment in the second aspect of the invention;

FIG. 2 is a graph showing the crystallization temperature and theelectron carrier concentration of a crystalline oxide according toFilm-forming Example 1;

FIG. 3 is a graph showing the electron carrier concentration and theelectron mobility of a crystalline oxide according to Film-formingExample 1;

FIG. 4 is a schematic view of a sputtering apparatus which was used forpreparing a crystalline oxide according to Film-forming Example 2;

FIG. 5 is a graph showing the atomic ratio and the electric resistivityof added metals in the crystalline oxide in Film-forming Example 2;

FIG. 6 is a schematic view of essential parts for explaining the methodfor producing a field-effect thin film transistor which is asemiconductor device according to one embodiment in the second aspect ofthe invention, in which (a) is a cross-sectional view showing the statein which a gate electrode is formed, (b) is a cross-sectional viewshowing the state in which a gate-insulating film is formed, and (c) isa cross-sectional view showing the state in which a crystalline oxide isformed;

FIG. 7 is a current-voltage characteristics graph of a field-effect thinfilm transistor according to Preparation Example;

FIG. 8 is a schematic cross-sectional view of essential parts of atop-gate type field-effect thin film transistor which is a semiconductordevice according to one embodiment in the second aspect of theinvention;

FIG. 9 is an X-ray chart of a target produced in Example 1;

FIG. 10 is an X-ray chart of a target produced in Example 2;

FIG. 11 is an X-ray chart of a target produced in Example 3;

FIG. 12 is an X-ray chart of a target produced in Example 4;

FIG. 13 is an X-ray chart of a target produced in Example 5; and

FIG. 14 is an X-ray chart of a target produced in Comparative Example 1.

BEST MODE FOR CARRYING OUT THE INVENTION

The sputtering target and the oxide semiconductor film in the firstaspect of the invention will be described below.

The sputtering target of the invention (hereinafter, often abbreviatedas “the target of the invention”) is an oxide sintered body containingindium (In) and at least one element selected from gadolinium (Gd),dysprosium (Dy), holmium (Ho), erbium (Er) and ytterbium (Yb), and theoxide sintered body is substantially of a bixbyite structure.

When the target of the invention contains an element other than indium(In), gadolinium (Gd), dysprosium (Dy), holmium (Ho), erbium (Er) andytterbium (Yb), crystals having a structure other than a bixbyitestructure may be generated in the target, and the career mobility of theoxide semiconductor film may be lowered.

A bixbyite structure will be explained. A bixbyite is also called arare-earth oxide C type or Mn₂O₃(I) type oxide. As described in“Technology of Transparent Conductive Film”, (published by Ohmsha,edited by the Japan Science and Technology Agency, 166 committee onTransparent Oxide and Photoelectronic Material, 1999 and so on), thestoicheiometric ratio of a bixbyite is shown by M₂X₃ (M is a cation andX is an anion, normally an oxygen ion) and an unit cell is constitutedby 16 M₂X₃ molecules, i.e. 80 atoms in total (M: 32 and X: 48). Ofthese, the bixbyite structure compound, which is the componentconstituting the target of the invention, is shown by In₂O₃, i.e., acompound showing No. 06-0416 peak pattern or a pattern similar (shifted)to this in JCPDS (Joint Committee on Powder Diffraction Standards)database in an X-ray diffraction. In addition, the bixbyite structurecompound includes a substitutional solid solution in which part of atomsand ions contained in a crystal structure is substituted by other atoms,or an interstitial solid solution in which other atoms are added intointerstitial sites.

Crystal states of compounds contained in a sintered body can bedetermined by observing the sample collected from a sintered body by anX-ray diffraction.

In the invention, “the sintered body being substantially of a bixbyitestructure” means a case where only a peak derived from a bixbyitestructure compound is observed in an X-ray diffraction.

In the target of the invention, an atomic ratio represented by M/(In +M)is preferably 0.01 to 0.25, wherein M is the content of gadolinium (Gd),dysprosium (Dy), holmium (Ho), erbium (Er) and ytterbium (Yb).

When the atomic ratio of M/(In +M) is less than 0.01, the oxidesemiconductor film may not be sufficiently stable. When the atomic ratioof M/(In +M) exceeds 0.25, the target may become an insulating body.

The target of the invention further contains a positive divalent metalelement. Stable semiconductor properties can be attained even when acrystalline oxide semiconductor film obtained from the target is a thinfilm if the target contains the positive divalent metal element.

The content of the positive divalent metal element is preferably 1 to 10at % relative to the total metal elements contained in the sputteringtarget. When the content is less than 1 at %, effects brought by thepositive divalent metal element may be small. On the other hand, whenthe content exceeds 10 at %, it may be difficult for the oxidesemiconductor film to crystallize.

Examples of the positive divalent metal element include Co, Ni, Cu, Pg,Pt, Ag, Au, Zn and Mg. Preferred are Zn and Mg.

The type of the positive divalent metal element does not limited to one,and one or a plural kinds of the positive divalent metal elements may becontained in the target of the invention.

Preferably, an alkaline earth metal element other than Mg and an alkalimetal element are not contained. The content of the alkaline earth metalelement other than Mg and the alkali metal element is 100 ppm or less,preferably 10 ppm or less, and more preferably 1 ppm or less, relativeto the total metal elements contained in the sputtering target. When thetarget contains the above-mentioned metal element in an amount exceeding100 ppm, in the case where the oxide semiconductor film obtained fromthe target is driven as a transistor, the semiconductor properties mayvary during driving the transistor for a long period of time, wherebythe on/off ratio and the driving threshold voltage may vary.

The target of the invention preferably further contains a metal elementwith an atomic valency of positive tetravalency or higher. A bulkresistance of the target can be decreased when the target contains ametal element with an atomic valency of positive tetravalency or higher,whereby the conductivity of the target increases and stable sputteringcan be conducted even by a DC sputtering method.

The content of the metal element with an atomic valency of tetravalencyor higher is preferably 100 to 2000 ppm in atomic ratio relative to thetotal metal elements contained in the sputtering target. When thecontent is less than 100 ppm, effects brought by the metal with anatomic valency of positive tetravalency or higher may be small. On theother hand, when the content exceeds 2000 ppm, carriers may be generatedin the oxide semiconductor film obtained from the target, wherebycarrier control may become difficult.

Examples of the metal element with an atomic valency of positivetetravalency or higher include Sn, Zr, Ge, Ti, Ce, Nb, Ta, Mo and W,with Ge, Ti, Zr, Nb and Ce being preferable.

An oxide semiconductor film obtained by using the sputtering target ofthe invention can be crystallized at a relatively low temperature asmentioned below. In such an oxide semiconductor film, the metal elementwith an atomic valency of tetravalency or higher contained in the targetis preferably a metal element which does not function as a dopant. Themetal element which does not function as a dopant is one having aneffect of decreasing the bulk resistance (not increasing carriers) inthe crystalline oxide semiconductor film. The metal element with anatomic valency of positive tetravalecy or higher having such effectsincludes Ti, Zr, Nb and Ce. The metal element with an atomic valency ofpositive tetravaleny or higher which does not decrease the carriermobility of the crystalline oxide semiconductor film are Nb and Ce.

The type of the metal element with an atomic valency of positivetetravalency or higher does not limited to one, and one or a pluralkinds of a metal element with an atomic valency of positive tetravalencyor higher may be contained in the target of the invention.

The sputtering target of the invention consists essentially of an oxideconsisting of indium (In), and at least one element selected fromgadolinium (Gd), dysprosium (Dy), holmium (Ho), erbium (Er) andytterbium (Yb), and optionally a positive divalent metal element and/ora metal element with an atomic valency of positive tetravalency orhigher. Alternatively, the sputtering target of the invention mayconsist thereof. The term “consist essentially of” means that thesputtering target of the invention is formed of an oxide comprisingindium (In), and at least one element selected from gadolinium (Gd),dysprosium (Dy), holmium (Ho), erbium (Er) and ytterbium (Yb), andoptionally a positive divalent metal element and/or a metal element withan atomic valency of positive tetravalency or higher, and othercomponents may be contained therein within a range which does not impairthe advantageous effects of the invention.

The sputtering target of the invention can be prepared by mixing andpulverizing material powders (raw material powders comprising indiumoxide, at least one of gadolinium oxide, dysprosium oxide, holmiumoxide, erbium oxide and ytterbium oxide to obtain a mixture, molding themixture into a desired shape to obtain a shaped body, and sintering theshaped body.

In the above-mentioned method for producing a sputtering target of theinvention, it is preferable to further add a material containing apositive divalent metal element and/or a metal element with an atomicvalency of tetravalency or higher to the above-mentioned raw materialpowers.

As examples of the material containing a positive divalent metal elementand/or a metal element with an atomic valency of positive tetravalencyor higher, metals themselves or oxides of the above-mentioned positivedivalent metal element and metal element with an atomic valency ofpositive tetravalency or higher can be used.

As for the positive divalent metal element and/or the metal element withan atomic valency of positive tetravalency or higher to be added, one ora plural kinds may be appropriately selected from the above-mentionedpositive divalent metal elements and/or metal elements with an atomicvalency of positive tetravalency or higher.

In the raw material powder, as for the amount ratio of a compoundselected from indium oxide, gadolinium oxide, dysprosium oxide, holmiumoxide, erbium oxide and ytterbium oxide, mixing is conducted such thatthe atomic ratio shown by M/(In +M) becomes 0.01 to 0.25 wherein M isthe content of gadolinium, dysprosium, holmium, erbium and ytterbium.

When a material containing a positive divalent metal element is added tothe raw material powder, the material containing the positive divalentmetal element is added such that the amount of the positive divalentmetal element becomes 1 to 10 at % relative to the total metal elementsin the raw material powder.

When a material with a metal element with an atomic valency of positivetetravalency or higher is added to the raw material powder, the materialcontaining the metal element with an atomic valency of positivetetravalency or higher is added such that the amount of the metalelement with an atomic valency of positive tetravalency or higherbecomes 100 to 2000 ppm in atomic ratio relative to the total metalelements in the raw material powder.

In the method for producing the sputtering target of the invention,other components may be added insofar as the advantageous effects of theinvention are not impaired.

After pulverizing the raw material powder by a dry beads mill or thelike, for example, the pulverized raw material is then molded into adesired shape. For molding, known molding methods such as pressuremolding and cold isostatic pressing or the like can be applied.

Subsequently, the molded product which has been shaped into a desiredshape is sintered to obtain a sintered body. It is preferred thatsintering be performed at 1200 to 1700° C. for 2 to 100 hours.

If sintering temperature is less than 1200° C., sintering density is notincreased, and the resistance value of the target itself is lowered, andabnormal discharge or the like may occur during sputtering. If thesintering temperature exceeds 1700° C., indium oxide is decomposed. As aresult, the target may be cracked, making the target productionimpossible.

This sintered body is substantially of a bixbyite structure. This can beconfirmed from the fact that only a peak derived from a bixbyitestructure compound is observed as a result of an X-ray diffractionanalysis of the sintered body.

The sputtering target of the invention can be produced by polishing orthe like the above-mentioned sintered body. As the method of polishing,known polishing technique such as mechanical polishing, chemicalpolishing, mechano-chemical polishing (combination of mechanicalpolishing and chemical polishing) or the like may be used.

In the method for producing the sputtering target of the invention, theresulting sputtering target may be subjected to a cleaning treatment.

As the cleaning treatment, air blowing, cleaning with running water orthe like can be given. For example, if cleaning is conducted by air blow(removal of foreign matters), foreign matters can be removed moreeffectively if air intake is conducted by means of a dust collector fromthe side opposite to the air blow nozzle.

If a thin film is formed by using the sputtering target of theinvention, an oxide semiconductor film of the invention can be producedby further subjecting this thin film to a heat treatment.

As the film-forming method, the RF magnetron sputtering method, DCmagnetron sputtering method, electron beam deposition method, ionplating method or the like can be used. Since the sputtering target ofthe invention has improved conductivity, it is possible to use the DCmagnetron sputtering method which is industrially advantageous.

The above-mentioned sputtering can be conducted in an inactive gasatmosphere such as 100% argon gas. It is also possible to conductsputtering in an argon gas atmosphere to which a slight amount of oxygen(about 20% of the sputtering gas) is added.

The oxide semiconductor film can be crystallized by heating atrelatively low temperatures. Heating is normally conducted at 150° C. to400° C., preferably 180° C. to 300° C., and more preferably 200° C. to250° C.

Heat treatment is preferably conducted for 1 minute to 10 hours.

The above-mentioned heat treatment may be conducted in an air or whilesupplying oxygen. As a result, the resulting oxide semiconductor filmcan have a more stable oxide structure.

In addition, the above-mentioned heat treatment can be conducted byheating the substrate of a thin film during the formation of the thinfilm. Heat treatment can be conducted by heating the substrate afterforming a thin film and processing such as etching or the like.

The oxide semiconductor film of the invention as obtained above containsindium, and at least one element selected from gadolinium, dysprosium,holmium, erbium and ytterbium, and is substantially of a bixbyitestructure.

The oxide semiconductor film of the invention can be crystallized atrelatively low temperatures, and hence, can stabilize oxygen in thecrystal. That is, the oxide semiconductor film of the invention suffersonly a slight degree of oxygen deficiency. Accordingly, in the oxidesemiconductor film of the invention, it is possible to suppressgeneration of carriers caused by oxygen deficiency. For example, theoxide semiconductor film of the invention has stable semiconductorproperties, i.e., having a carrier density of 1.0×E¹⁷ cm⁻³ order orless, an on/off ratio of 10⁴ order or more and showing normally-offproperties.

The semiconductor device in the second aspect of the invention will bedescribed in detail.

One Embodiment of the Semiconductor Device

FIG. 1 is a schematic cross-sectional view of essential parts of afield-effect thin film transistor which is a semiconductor deviceaccording to one embodiment of the invention.

In FIG. 1, a field-effect thin film transistor 1 (hereinafterabbreviated as a “TFT1”) is provided with a gate electrode 25 formed ona glass substrate 10, a gate-insulating film 24 formed on the glasssubstrate 10 and gate electrode 25, a crystalline oxide 21 as thechannel layer formed on the gate-insulating film 24 above the gateelectrode 25, and the source electrode 22 and the drain electrode 23formed separately on the crystalline oxide 21 and the gate-insulatingfilm 24. The TFT 1 is not limited to the bottom-gate type TFT asmentioned above, and a TFT with various configurations such as atop-gate type TFT may be used. The substrate on which the TFT 1 isformed is not limited to the transparent glass substrate 10, and it maybe a resin substrate and a resin film having flexibility. It may be asemitransparent or light-shielding substrate.

In the TFT1, the crystalline oxide 21 containing In (indium) is used asan N-type semiconductor (a channel layer in this embodiment). Theelectron carrier concentration of the crystalline oxide 21 is less than10¹⁸/cm³. The reason for allowing the electron carrier concentration tobe less than 10¹⁸/cm³ is that, if the crystalline oxide 21 with anelectron carrier concentration of 10¹⁸/cm³ or more is used as thechannel layer of the TFT1, the on-off ratio cannot be increasedsufficiently. If no gate voltage is applied to the TFT1, a large amountof current tends to be flown between the source electrode 22 and thedrain electrode 23, and a normally-off operation cannot be attained.That is, as the active layer of the TFT1, when the TFT1 in which thecrystalline oxide 21 with an electron carrier concentration of less than10¹⁸/cm is used, the TFT1 with desired properties can be obtained.

The electron carrier concentration of the crystalline oxide 21 of theinvention is a value measured at room temperature. The room temperatureis, for example, 25° C. Specifically, it is a temperature which can beappropriately selected from a range of about 0 to 40° C. The electroncarrier concentration of the crystalline oxide 21 according to theinvention is not necessarily less than 10¹⁸/cm³ in the entiretemperature range of about 0 to 40° C. For example, it suffices that acarrier electron concentration of less than about 10¹⁸/cm³ be realizedat 25° C. In addition, preferably, the carrier electron concentration isfurther lowered to about 10¹⁷/cm³ or less, more preferably about10¹⁶/cm³ or less. With this range, a normally-off TFT1 can be obtainedin a high yield.

The lower limit of the electron carrier concentration in the crystallineoxide 21 is not particularly limited as long as it can be applied as thechannel layer of a TFT. Therefore, in the invention, by controllingmaterials, composition ratio, production conditions, post-treatmentconditions or the like of the crystalline oxide as in the examplesmentioned later, for example, the electron carrier concentration isallowed to be 10¹²/cm³ or more and less than 10¹⁸/cm³. Further, it ispreferred that the electron carrier concentration be 10¹³/cm³ or moreand 10¹⁷/cm³ or less, more preferably 10¹⁵/cm³ or more and 10¹⁶/cm³ orless. With this range, a normally-off TFT1 having prescribed electronmobility can be obtained in a high yield.

The electron carrier concentration can be measured by the Hall effectmeasurement. It is preferred to perform the AC Hall measurement whenmeasuring an electron carrier concentration of less than about 10¹⁷/cm³.The reason therefor is that, in the case of the DC Hall measurement,there is a large degree of variation in measurement values, which maycause measurement reliability to be deteriorated.

The channel layer of the TFT1 (semiconductor thin film) is a thin filmcontaining a crystalline substance (that is, the crystalline oxide 21).As for the crystalline oxide 21, at least part or all of thesemiconductor thin film is crystalline. As a result, as compared withthe case where the semiconductor thin film is amorphous, the carrierconcentration can be decreased or controlled easily, and the operationof the TFT1 becomes stable. As a result, the performance of the TFT1such as stability, uniformity, reproducibility, heat resistance anddurability can be improved.

The crystalline substance to be contained in the thin film may be eithersingle crystalline or polycrystalline (including an epitaxial film). Apolycrystalline film which is easily manufactured on the industrialbasis and can be increased in area is preferable. A polycrystal ispreferable, since a single crystal film may have cracks by bending orimpact during the production process or use. In the invention, thecrystalline oxide 21 means an oxide showing specific diffraction linesin X-ray diffraction spectrum. An amorphous oxide means an oxide showinghalo pattern and no specific diffraction lines.

Furthermore, it is preferred that the energy band gap between theconduction band and the valence band of the semiconductor thin filmaccording to the present invention be about 2.8 eV or more. Due to sucha band gap, a disadvantage that electrons of the valence band areexcited to allow current leakage to occur frequently by the irradiationwith visible rays can be effectively avoided.

It is preferred that the crystalline oxide 21 be a non-degeneratesemiconductor.

In this way, an off current can be rendered small and an on/off ratiocan be rendered large.

The above-mentioned crystalline oxide 21 contains a positive divalentelement.

Due to the presence of the positive divalent element, the electroncarrier concentration can be decreased due to the effects ofextinguishing carriers caused by oxygen deficiency. In addition, asknown by ITO or the like, the average free process of carriers does notdepend on the size of the crystal particles, since it is smaller thanthe size of crystalline particles in the crystalline state. For thisreason, the crystalline oxide 21 can be a crystalline thin film with ahigh electron mobility. In addition, since the added element is adivalent metal element, it cannot be a scattering factor, the electronmobility can be kept high.

The electron mobility of a thin film formed of the crystalline oxide 21is inferior to that of a single crystal, but the thin film can have agreat electron mobility. Further, by containing a positive divalentelement, a thin film composed of the crystalline oxide 21 can be morestabilized. In addition, it has a high field effect mobility, and thecomposition range for a stable crystalline oxide can be expanded.

In the meantime, the above-mentioned positive trivalent element and theabove-mentioned positive divalent element respectively mean an elementwhich can take positive trivalence and positive divalence, respectivelyin the ionic state.

It is preferred that the above-mentioned positive divalent element be atleast one element selected from Zn, Mg, Ni, Co and Cu.

In this way, indium is solid-solution-substituted by at least part of apositive divalent element such as zinc, whereby the electron carrierconcentration can be effectively lowered. There are no restrictions onthe solid-solution-substituted amount of a metal such as zinc. Itsuffices that part of the metal be solid-solution-substituted. Thecrystalline oxide 21 may be an oxide mixture.

Zinc and other divalent metals such as Mg, Ni, Co and Cu may be addedsimultaneously. For example, when Zn and Mg are added simultaneously, ascompared with the case where Zn is added alone, the electron mobility isincreased. The degree of increase in electron mobility is about 10cm²/(V·sec) at room temperature. It is an increase which is larger thanan amorphous silicon by one digit. Further, when film formation isconducted at the same conditions, electronic resistivity increases withan increase in the Mg content, whereby electron mobility decreases. Itis preferred that the content of a positive divalent element composed ofZn and Mg be exceeding 0.5 at % and less than 10 at %. The reasontherefor is as follows. If the content of the positive divalent elementis less than 0.5 at %, the electric resistance cannot be improved evenwhen crystallized. If the content of the positive divalent element is 10at % or more, it cannot be crystallized easily, and it becomes necessaryto set a high crystallization temperature. As a result, a large amountof energy is consumed, which is economically disadvantageous.

Further, it is preferred that the atomic ratio of the number of atoms ofthe positive divalent element ([M2]) to the number of atoms of the totalmetal element ([A]) contained in the crystalline oxide 21 be:

0.001≦[M2]/[A]<0.2

In this way, a more stable crystalline oxide can be obtained. Further,the electron carrier concentration can be controlled to less than10¹⁸/cm³.

As the positive divalent element, normally, at least one of Zn, Mg, Ni,Co and Cu is used. As for the added amount of Zn, Mg, Ni, Co and Curelative to the total metal elements of the crystalline oxide 21 is 0.1at % or more and less than 20 at %. The reason therefor is that, if thecontent is less than 0.1 at %, effects of addition are small, and theremay be a case where the electron carrier concentration cannot belowered. If the content is 20 at % or more, the crystallizationtemperature becomes too high to be put into practical use. It ispreferred that the atomic range be 0.005≦[M2]/[A]<0.1, more preferably0.01≦[M2]/[A]<0.08. Substantially the similar effects can be obtained ifMg is selected instead of Zn. Zn, Mg, Ni, Co and Cu exhibit almostsimilar effects.

In the above-mentioned description, the amount of carriers generated byoxygen deficiency is suppressed by the amount of the divalent metalelement contained in the crystalline oxide 21. That is, after the filmformation, it is preferable to control carriers by crystallization andthe amount of oxygen deficiency (decrease or increase) by reaction withthe oxygen of air, by subjecting an indium oxide film to a posttreatment in an atmosphere containing oxygen to crystallize the film. Inorder to control the amount of oxygen deficiency effectively, thetemperature of the oxygen-containing atmosphere may preferably be 150°C. or more and 500° C. or less, preferably 200° C. or more and 300° C.or less, further preferably 250° C. or more and 300° C. or less. It isalso preferable to conduct crystallization and a reaction with oxygensimultaneously.

By controlling carriers and extinguishing oxygen deficiency byconducting film formation in an atmosphere containing oxygen, followedby a heat treatment for crystallization, a prescribed electron carrierconcentration (less than 10¹⁸/cm³) may be attained, and a past treatmentmay be conducted in an atmosphere containing oxygen after the filmformation. As long as the prescribed electron carrier concentration(less than 10¹⁸/cm³) is attained, it is better not to conduct oxygenpartial pressure control and to conduct a post treatment in anatmosphere which does not contain oxygen.

The above-mentioned crystalline oxide 21 may contain a positivetrivalent element other than the indium instead of the positive divalentelement.

Also in this way, due to the effects of extinguishing carriers generatedby oxygen deficiency, it is possible to decrease the electron carrierconcentration. Further, although being inferior to that of a singlecrystal, the electron mobility of a thin film formed of the crystallineoxide 21 can be high. In addition, by containing a positive trivalentelement, a thin film formed of the crystalline oxide 21 is morestabilized. The film has a high field effect mobility, and thecomposition range for a stable crystalline oxide can be expanded.

A configuration is not limited to one in which either one of theabove-mentioned positive divalent element and the above-mentionedpositive trivalent element is contained. However, it may be aconfiguration in which the above-mentioned positive divalent element andthe above-mentioned positive trivalent element are contained. In thisway, generation of carriers can be suppressed further effectively.

In the In-containing crystalline oxide 21, oxygen and metal ions aresubjected to ionic bonding. Therefore, a divalent or trivalent metaloxide cannot be an ionic carrier scattering factor. That is, theelectron mobility of the crystalline oxide 21 containing at least oneelement of Zn, Mg, Ni, Co and Cu, or at least one element of B, Al, Ga,Sc, Y and a lanthanoid element; or at least one element of Zn, Mg, Ni,Co and Cu, and at least one element of B, Al, Ga, Sc, Y and a lanthanoidelement is, although being inferior to that of a single crystal, almostequivalent to that of a single crystal.

Further, it is preferred that the above-mentioned positive trivalentelement be at least one element of B, Al, Ga, Sc, Y and a lanthanoidelement.

In this way, the crystalline oxide can be effectively stabilized due tostrong ion bonding property of B, Al, Ga, Sc, Y and a lanthanoidelement. In the case of a composite indium oxide consisting of ions witha small difference in ionic radius, the crystalline phase can be morestabilized. For example, in the case of the In-lanthanoidelement-oxygen-based crystalline oxide 21, the ionic radius decreasesand gets closer to the ionic radius of indium with an increase in theatomic number of a lanthanoid element. In this way, in the case of anion with a small atomic number, it is difficult to obtain a crystallineindium oxide film which is stable even though it is subjected to a heattreatment. However, by adding In and a lathanoid element in an amountratio of 0.5 at % to 10 at % relative to the total metal elements, astable crystalline film can be obtained easily. On the other hand, inthe case of an ion with a large atomic number, it is easy to obtain acrystalline indium oxide film which is stable even though it issubjected to a heat treatment. By adding In and a lanthanoid element inan amount ratio of 0.5 at % to 10 at % relative to the total metalelements, a significantly stable crystalline film can be obtained.

In addition, B, Al, Ga, Sc, Y and a lanthanoid element has a strongbonding power with oxygen (the work function of a metal is smaller thanthe work function of an In metal), and an oxygen deficiency does notoccur easily. Further, by adding at least one element of Zn, Mg, Ni, Coand Cu to form a composite indium oxide, carriers generated by partialoxygen deficiency can be controlled and carriers are not generatedeasily.

It is preferred that the atomic ratio of the number of atoms of thepositive trivalent element ([M3]) to the number of atoms of the totalmetal element ([A]) contained in the crystalline oxide 21 be:

0.001≦[M3]/[A]<0.2

In this way, a more stable crystalline oxide can be obtained. Inaddition, the electron carrier concentration can be controlled to lessthan 10¹⁸/cm³.

As the positive trivalent element, at least one element of B, Al, Ga,Sc, Y and a lanthanoid element is normally used.

As for the added amount of B, Al, Ga, Sc, Y and a lanthanoid elementrelative to the total metal elements in the crystalline oxide 21 is 0.1at % or more and less than 20 at %. The reason therefor is that, if theadded amount is less than 0.1 at %, effects of addition is small, andthe electron carrier concentration may not be decreased. If the addedamount is 20 at % or more, the crystallization temperature becomes toohigh to be put into practice. Preferably, the atomic ratio is0.005≦[M3]/[A]<0.1, more preferably 0.01≦[M3]/[A]<0.08. For example, ifY is selected instead of B, almost similar effects can be obtained. B,Al, Ga, Sc, Y and a lanthanoid element exhibits almost similar effects.

The crystalline oxide 21 containing the positive divalent element or thepositive trivalent element can be formed into a film by a sputteringmethod, for example.

Then, Film-formation Example 1 of a thin film of the crystalline oxide21 is explained.

Film-Formation Example 1

Using as a target a polycrystalline sintered body having an indium oxidecomposition containing at least one of Zn, Mg, Ni, Co and Cu; or atransparent indium oxide composition containing B, Al, Ga, Sc, Y and alanthanoid element, the above-mentioned crystalline oxide 21 can beformed by a sputtering method. Generally, as the method of forming acrystalline indium oxide film, a vapor phase method such as a pulselaser deposition method (PLD method), the sputtering method (SP method),the electron beam deposition method or the like are used. In the PLDmethod, it is easy to control the composition of materials, and the SPmethod is excellent in respect of mass productivity. The film-formationmethod is, however, not particularly limited.

In the above-mentioned polycrystalline target, it is possible to use asintered body target having an indium oxide composition containing atleast one of Zn, Mg, Ni, Co and Cu; or an indium oxide compositioncontaining B, Al, Ga, Sc, Y and a lanthanoid element (size: 4 inches indiameter, 5 mm in thickness). This can be produced by subjecting, asstarting materials, In₂O₃ and at least one of Zn, Mg, Ni, Co and Cu orat least one of B, Al, Ga, Sc, Y and a lanthanoid element (4N reagent,each) to wet mixing (solvent: ethanol), granulating, single-axial pressmolding or a cold static press molding, and sintering (at 1450° C. for36 hours).

As for the In₂O₃ targets produced by the above-mentioned method, thespecific resistance of an In₂O₃ target in which 5 wt % of Zn was addedin terms of ZnO, the specific resistance of an In₂O₃ target in which 3wt % of Mg was added in terms of MgO, the specific resistance of anIn₂O₃ target in which 2 wt % of Ni was added in terms of NiO, thespecific resistance of an In₂O₃ target in which 2 wt % of Co was addedin terms of CoO, the specific resistance of an In₂O₃ target in which 1wt % of Cu was added in terms of CuO, the specific resistance of anIn₂O₃ target in which 2 wt % of B was added in terms of B₂O₃, thespecific resistance of an In₂O₃ target in which 2 wt % of Al was addedin terms of Al₂O₃, the specific resistance of an In₂O₃ target in which 4wt % of Ga was added in terms of Ga₂O₃, the specific resistance of anIn₂O₃ target in which 3 wt % of Sc was added in terms of Sc₂O₃, thespecific resistance of an In₂O₃ target in which 3 wt % of Y was added interms of Y₂O₃, the specific resistance of an In₂O₃ target in which 1 wt% of a trivalent lanthanoid element was added in terms of a trivalentlanthanoid element oxide was almost 0.005 (Ωcm).

The ultimate vacuum of a film-forming room was allowed to be 5×10⁻⁶ Pa,and an argon gas (containing 3% of oxygen) was controlled to 0.3 Pa. Byallowing the substrate temperature to be room temperature, filmformation was conducted by a sputtering method using the above-mentionedtargets. As a result, an indium oxide thin film with a thickness of 100nm was obtained within about 40 minutes. It is preferred that thesputtering pressure be controlled to about 0.1 Pa or more and less than2.0 Pa.

For the thus obtained thin film, grazing incidence X-ray diffraction(the thin film method, incidence angle: 0.5 degree) of the thin film wasperformed. No clear diffraction peak was observed. From this fact, itwas confirmed that each of the produced indium oxide thin films wasamorphous. After heating these thin films at 200° C. or higher in airfor one hour, grazing incidence X-ray diffraction (the thin film method,incidence angle: 0.5 degree) of the thin film was performed. In eachthin film, a clear diffraction peak was observed. From this fact, it wasconfirmed that each of the produced indium oxide films was crystallized.As a result, a thin film formed of the crystalline oxide 21 wasobtained.

Further, as a result of an X-ray reflectance measurement to analyze thepattern, the average root mean square resistance (Rrms) of each of thethin films was about 0.8 nm. The specific resistance of each of the thinfilms was about 10² Ωcm or more. From this, it was assumed that theelectron carrier concentration was about 10¹⁶/cm³ and the electronmobility was about 7 cm²/(V·sec).

The electron carrier concentration was measured by means of a Hallmeasurement apparatus manufactured by Toyo Corporation.

From the analysis of a light absorption spectrum, the forbidden bandenergy width of the thus obtained amorphous thin film was found to beabout 3.2 eV. Further, as a result of a measurement by means of aspectrophotometer, this semiconductor thin film had a transmittance tolight having a wavelength of about 400 nm of about 85%, which means thatthe semiconductor thin film was excellent also in transparency.

From the above, the produced crystalline oxide 21 was a lowelectroconductive, transparent, and flat thin film which suffered only aslight degree of oxygen deficiency.

The crystalline oxide 21 in the above-mentioned Film-formation Example 1was formed into a film at low temperatures, and an oxide formed into afilm at these temperatures is amorphous. Therefore, the crystallineoxide 21 can be prepared by crystallizing by heating an oxide which hasbeen formed into a film in an amorphous state.

Then, the measurement results of the crystallization temperature and theelectron carrier concentration of the crystalline oxide 21 will beexplained with reference to the drawings.

[Measurement Results of the Crystallization Temperature and the ElectronCarrier Concentration of the Crystalline Oxide]

FIG. 2 is a graph showing the crystallization temperature and theelectron carrier concentration of a crystalline oxide according to theFilm-forming Example 1.

In FIG. 2, a thin line indicates the crystalline oxide 21 in which toindium oxide are added a positive divalent element (Zn, Mg, Ni, Co andCu, with Zn being as a representative example) (appropriatelyabbreviated as a crystalline oxide indicated by a thin line). For thecrystalline oxide indicated by the thin line, a sputtering targetcontaining about 5 wt % of zinc oxide, with the remaining being indiumoxide was used. In air, a heat treatment was conducted at eachtemperature for one hour to measure the carrier concentration by a Hallmeasurement. At the same time, using the same sample, crystallineproperties were confirmed by an X-ray diffraction method.

The dotted line indicates the crystalline oxide 21 in which to indiumoxide are added a positive trivalent element (B, Al, Ga, Sc, Y, La, Nd,Sm, Eu, Gd, Dy, Ho, Er, Tm, Yb and Lu, with Yb being as a representativeexample) (appropriately abbreviated as a crystalline oxide indicated bya dotted line) other than the above-mentioned indium. For thecrystalline oxide indicated by the dotted line, a sputtering targetcontaining about 1 wt % of ytterbium oxide, with the remaining beingindium oxide was used. In air, a heat treatment was conducted at eachtemperature for one hour to measure the carrier concentration by a Hallmeasurement. At the same time, using the same sample, crystallineproperties were confirmed by an X-ray diffraction method.

Further, a thick broken line indicates a crystalline oxide composed onlyof indium oxide (appropriately, abbreviated as a crystalline oxideindicated by the broken line).

The crystalline oxides indicated by a thin line, the crystalline oxideindicated by a dotted line and the crystalline oxide indicated by abroken line were produced in substantially the same manner as in theabove-mentioned Film-forming Example 1, except for the crystallizationtemperature or the like. The electron carrier concentration relative tothe crystallization temperature was measured.

As for the crystalline oxide indicated by a thin line, the electroncarrier concentration suddenly lowered at a crystallization temperatureof about 200° C., and such a lowering stopped at about 230° C. Ifcrystallized at about 250° C., the electron carrier concentration wasabout 5×10¹⁵/cm³. As a result of observation by means of an X-raydiffraction, the oxide which was subjected to a heating treatment at atemperature of 180° C. or higher, a clear peak was observed, and hence,it was confirmed that this oxide was of a bixbyite structure. Further,similar results were obtained when similar observations were conductedby adding about 5 at % of Mg, Ni, Co or Cu instead of Zn.

As for the crystalline oxide indicated by a dotted line, the electroncarrier concentration suddenly lowered from the crystallizationtemperature of about 200° C., and such a lowering stopped at about 230°C. When crystallized at about 250° C., the electron carrierconcentration was about 10¹⁶/cm³. As a result of observation by means ofan X-ray diffraction, the oxide which was subjected to a heatingtreatment at a temperature of 180° C. or higher, a clear peak wasobserved, and hence, it was confirmed that this oxide was of a bixbyitestructure. Further, similar results were obtained when similarobservations were conducted by adding about 4 at % of B, Al, Ga, Sc, Y,La, Nd, Sm, Eu, Gd, Dy, Ho, Er, Tm or Lu instead of Yb.

As for the crystalline oxide indicated by a broken line, the electronconcentration suddenly lowered from the crystallization temperature ofabout 220° C., and such a lowering stopped at about 240° C. Ifcrystallized at about 250° C., the electron carrier concentration wasabout 10¹⁹/cm³.

That is, the crystalline oxide indicated by the dotted line and thecrystalline oxide indicated by the thin line could have an electroncarrier concentration which is preferable as a semiconductor (less thanabout 10¹⁸/cm³) by controlling their crystallization temperatures.

The crystalline oxide indicated by a broken line started to crystallizeat about 160° C. That is, by heating to about 160° C., a peak wasobserved in an X-ray diffraction, which means the start ofcrystallization. In the case of the crystalline oxide indicated by thethin line and the crystalline oxide indicated by the dotted line, theadded amount may be set to be smaller when the crystallizationtemperature is set to be a low temperature. When the crystallinetemperature can be set to be a high temperature, the added amount may beset to be larger.

The Hall measurement apparatus and the Hall measurement conditions fordetermining an electron carrier concentration are as follows.

[Hall Measurement Apparatus]

Resi Test 8310: manufactured by Toyo Corporation

[Measurement Conditions]

Room temperature (about 25° C.), about 0.5 [T], about 10⁻⁴ to 10⁻¹² A,AC magnetic field Hall measurement

From the above-mentioned measurement results, in order to control theelectron carrier concentration effectively, the heat treatment ispreferably conducted at the temperature in an atmosphere containingoxygen of 150° C. or more and 500° C. or less, preferably 200° C. ormore and 300° C. or less, and further preferably 250° C. or more and300° C. or less.

By conducting the crystallization treatment in an atmosphere whichcontains oxygen in a prescribed concentration, crystallization can becontrolled effectively.

Further, although not shown, by further increasing the added amount ofthe positive divalent element or the positive trivalent element, and byforming into a film at high temperatures to allow crystallization to beconducted easily, and by conducting a heat treatment at hightemperatures, the electron carrier concentration could be furtherdecreased.

The lower limit of the electron carrier concentration in the inventionvaries depending on the application of the resulting indium oxide film,i.e. the device, circuit or apparatus in which the resulting indiumoxide film is used.

However, the lower limit is 10¹⁴/cm³, for example.

In this embodiment, at first, an amorphous oxide is formed at lowtemperatures, and then, heated to a crystallization temperature, therebyto obtain the crystalline oxide 21 with a desired carrier concentration.The manner is, however, not limited to this. For example, thecrystalline oxide 21 may be formed during film formation at hightemperatures.

The film formation may be conducted in an atmosphere containing oxygen,and the crystallization may be also conducted in an atmospherecontaining oxygen. As long as a prescribed electron carrierconcentration (less than 10¹⁸/cm³) can be obtained, no control on theoxygen partial pressure may be made during film formation and acrystallization treatment after the film formation may be conducted inan atmosphere containing oxygen.

[Measurement Results on the Electron Carrier Concentration and theElectron Mobility of the Crystalline Oxide]

Then, the measurement results on the electron carrier concentration andthe electron mobility of the resulting crystalline oxide 21 will beexplained with reference to the drawings.

FIG. 3 is a graph showing the electron carrier concentration and theelectron mobility of a crystalline oxide according to Film-formingExample 1.

In FIG. 3, the triangle indicates the crystalline oxide 21 in which apositive divalent element (for example, Zn in an amount of 5 wt % asconverted in ZnO) is added in indium oxide (appropriately abbreviated asthe crystalline oxide indicated by the triangle).

The diamond indicates the crystalline oxide 21 in which a lanthanoidelement (for example, Yb in an amount of 1 wt % as converted in Yb₂O₃)is added in indium oxide (appropriately abbreviated as the crystallineoxide indicated by the diamond).

The circle indicates the crystalline oxide 21 composed only of indiumoxide (appropriately abbreviated as the crystalline oxide indicated bythe circle).

The crystalline oxide indicated by the diamond and the crystalline oxideindicated by the triangle were prepared by controlling thecrystallization temperature, the content of a lanthanoid element or apositive divalent element or the like. Whether an electron carrierconcentration of less than 10¹⁸/cm³ can be attained or not depends onthe conditions of a heat treatment, the configuration of a film-formingapparatus, materials to be formed into a film, composition or the like.

The crystalline oxide indicated by the triangle and the crystallineoxide indicated by the diamond had an electron carrier concentration ofabout 10¹⁶/cm³ to about 10¹⁹/cm³, and an electron mobility of aboutseveral cm²/V·sec to several tens cm²/V·sec by controlling productionconditions (the crystallization temperature, the content or the like).

The crystalline oxide indicated by the circle had an electron carrierconcentration of about 10¹⁹/cm³ to about 10²⁰/cm³ and an electronmobility of about 100 cm²/V·sec although controlling productionconditions. Further, the above-mentioned crystalline oxide indicated bythe triangle and the above-mentioned crystalline oxide indicated by thediamond are merely one example. Although not shown, the crystallineoxide 21 having more improved properties could be prepared bycontrolling production conditions.

Normal compounds show a tendency that the electron mobility decreasesdue to the collision of electrons with an increase in the number ofelectrons. In contrast, in the case of the crystalline oxide indicatedby the diamond and the crystalline oxide indicated by the triangle, theelectron mobility logarithmically proportionally increases withincreased electron carrier concentration in an electron carrierconcentration range of about 1×10¹⁶ to 1×10¹⁸/cm³. That is, if theelectron carrier concentration (X coordinate) and the electron mobility(Y coordinate) are plotted in the graph of the both logarithms, theplotted points were almost on a straight line rising from the left tothe right. In addition, depending on the combination of a positivedivalent element or a positive trivalent element to be contained in thecrystalline oxide 21, the plotted points form almost straight differentlines rising from the left to the right.

By effectively utilizing these unique properties, the electron carrierconcentration or the electron mobility can be freely set to a desiredvalue. As a result, it is possible to provide the crystalline oxide 21which has more preferable semiconductor properties for varioussemiconductor devices. In addition, the added value of the semiconductordevice can be improved.

In this embodiment, the electron mobility of the crystalline oxide 21which is used as the channel layer of the field-effect thin filmtransistor 1 can exceed 1 cm²/(V·sec) or more, preferably exceed 5cm²/(V·sec). As a result, the saturation current after pinch-off can beallowed to exceed about 10 μA and an on-off ratio can be allowed toexceed about 10³. Further, the electron carrier concentration can beallowed to be less than 10¹⁸/cm³, preferably less than 10¹⁶/cm³. Thecurrent flown between the source electrode 22 and the drain electrode 23when the transistor is off (no gate voltage is applied) can be less thanabout 10 μA, preferably less than about 0.1 μA.

Further, as for the field-effect thin film transistor 1, a high voltageis applied to the gate electrode 25 in the pinch-off state, andhigh-density electrons are present in the crystalline oxide 21 as thechannel layer. Therefore, according to the invention, the saturationcurrent value can be increased in an amount corresponding to theincrease in the electron mobility. As a result, almost all transistorproperties are improved, i.e. an on-off ratio is increased, thesaturation current is increased, the switching speed is increased, orthe like.

The indium oxide (In₂O₃) film can be formed by the vapor phase method,and an amorphous film can be obtained by adding about 0.1 Pa of moisturecontent in an atmosphere during film formation. This amorphous indiumoxide film can be crystalline indium oxide by a heat treatment. However,in the case of an In₂O₃ film alone, although a crystalline film can beobtained, stable semiconductor properties cannot be exhibited even whenabout 30% of oxygen gas is introduced into an atmosphere during filmformation.

Film-Forming Example 2

In this film-forming example, the crystalline oxide 21 was formed into afilm by a direct current (DC) sputtering method using an argon gas as anatmospheric gas. The sputtering method is not limited to a directcurrent (DC) sputtering method. For example, film formation can beconducted by a RF (radio frequency) sputtering method.

FIG. 4 is a schematic view of a sputtering apparatus which was used forpreparing a crystalline oxide according to Film-forming Example 2.

In FIG. 4, in a sputtering apparatus 5, within a film-forming chamber51, a substrate holder 52 provided with cooling and heating mechanisms,a shutter 53, an electrode 54 and a shield 55 are provided. In addition,a main valve 511, a turbomolecular pump 512, an oil-rotating pump 513, aleak valve 514, a vacuum meter 515 or the like are provided in order toallow the inside of the film-forming chamber to be vacuum. In thefilm-forming chamber 51, an oxygen gas or an Ar gas is supplied througha barrier leak valve 516. In addition, the electrode 54 is installed inthe film-forming chamber 51 through an insulator 517, and electric poweris supplied from a DC power source 518, followed by cooling with coolingwater. In addition, a substrate 56 is installed on the substrate holder52, and a target 57 is put on the electrode 54.

As the substrate 56 for film formation, an SiO₂ glass substrate (1737manufactured by Corning) was prepared. As the treatment before the filmformation, this substrate 56 was subjected to ultrasonic degreasingcleaning for 5 minutes each with acetone, ethanol and ultrapure water,and dried at 100° C. in air. The substrate is preferably subjected to UVozone cleaning, whereby a film with good adhesion can be obtained.

As a target material, an indium oxide polycrystalline sintered bodycontaining In₂O₃(ZnO)₄ composition (size: 4 inches in diameter, 5 mm inthickness) was used.

In this sintered body, as a starting material, 99 wt % In₂O₃:1 wt % ZnO(4N reagent each) was subjected to wet mixing (solvent: ethanol),granulated by means of a spray drier, and molded using a single-axispressing machine. Further, cold isostatic pressing was conducted,following by main sintering (36 hours at 1450° C.). The thus preparedtarget had a specific resistance of 0.005 (Ωcm).

The ultimate pressure in the film-forming chamber 51 was 5×10⁻⁴ Pa. Thetotal pressure of the oxygen gas and the argon gas during film formationwas fixed within a range of 0.1 to 2.0 Pa. The partial pressure ratio ofan argon gas and an oxygen gas was changed to allow it to vary within anoxygen concentration of 1 to 30%.

The substrate temperature was room temperature, and the distance betweenthe target and the substrate for film formation was 80 mm. The substrateholder 52 was provided with a rotating mechanism, whereby a uniform thinfilm could be obtained by conducting film formation while rotating.

The input powder was DC 100 W and the film-forming speed was 5 nm/mm.

For the thus obtained thin film, grazing incidence X-ray diffraction(the thin film method, incidence angle: 0.5 degree) of the thin film wasperformed. No clear diffraction peak was observed. From this fact, itwas confirmed that each of the indium oxide thin films immediately afterproduced was amorphous. After heating these thin films at 200° C. orhigher, grazing incidence X-ray diffraction (the thin film method,incidence angle: 0.5 degree) of the thin film was performed. In eachthin film, a clear diffraction peak was observed, showing that this thinfilm was crystalline. The carrier concentration of this crystalline thinfilm was 0.8×10¹⁶/cm³, showing that this was less than 10¹⁶/cm³.

Further, as a result of an X-ray reflectance measurement to analyze thepattern, the average root mean square resistance (Rrms) of each of thethin films was about 0.8 nm. As a result of an analysis by the ICPmethod, the atomic ratio of the number of the atoms of Zn (=[Zn]) to thenumber of the atoms of total metal elements contained in the crystallineoxide ([A]) was [Zn]/[A]=0.018. In this film-formation Example, it wasfound that [A]=[In]+[Zn]. [In] is the number of the atoms of Incontained in the crystalline oxide.

[Measurement Results of the Ratio of Added Metals and the ElectricResistivity in the Crystalline Oxide]

Then, by varying the type, the composition or the like of the positivedivalent element and the positive trivalent element to be added, and byfurther controlling the preparation conditions, a plurality ofcrystalline oxides 21 were prepared.

Next, the measurement results of the ratio of added metals and theelectric resistivity (specific resistance) in parts of these crystallineoxides 21 will be explained with reference to the drawings.

FIG. 5 is a graph showing the atomic ratio of the added metals and theelectric resistivity in the crystalline oxide according to theFilm-forming Example 2.

In FIG. 5, the triangle indicates the crystalline oxide 21(appropriately abbreviated as the crystalline oxide indicated by thetriangle) in which a positive divalent element (M=at least one of Zn,Mg, Ni, Co and Cu. In FIG. 5, 5 wt % of Zn as converted to ZnO) is addedin indium oxide.

The diamond indicates the crystalline oxide 21 (appropriatelyabbreviated as the crystalline oxide indicated by the diamond) in whicha positive trivalent metal other than the indium (M=at least one of B,Al, Ga, Sc, Y, La, Nd, Sm, Eu, Gd, Dy, Ho, Er, Tm, Yb and Lu. In FIG. 5,1 wt % of Yb as converted to Yb₂O₃) is contained.

Further, the circle indicates the crystalline oxide composed only ofindium oxide (appropriately abbreviated as the crystalline oxideindicated by the circle).

In the above-mentioned crystalline oxide indicated by the triangle, whenthe atomic ratio of the number of the atoms of the positive divalentelement ([M]) to the number of the atoms of total metal elementscontained the crystalline oxide 21 ([A]) [M]/[A] is about 0.6% to 12.3%,the electric resistivity was about 2×10⁻² Ωcm to 10⁵ Ωcm. That is, byadding a slight amount of an added metal M which is a positive divalentelement, the electric resistivity could be improved to about 10² Ωcm ormore. By further increasing the atomic percentage, crystallization stopsto increase the electric resistance. For example, in the case of anindium oxide thin film containing 9.5 at % of zinc formed at a substratetemperature of 25° C. and an oxygen partial pressure of 3%, the electricresistance could be improved to about 10⁵ Ωcm. Further, in the case ofthe crystalline indium oxide film containing 10 at % or more of zinc,the electric resistance was lowered to become a conductive thin film.This conductive thin film was heat treated at 300° C. After performinggrazing incidence X-ray diffraction (the thin film method, incidenceangle: 0.5 degree) of the thin film, no clear diffraction peak wasobserved, showing that the indium oxide thin film was amorphous.

In the case of the above-mentioned crystalline oxide indicated by thediamond, when the atomic ratio % of the number of the atoms of thepositive trivalent element ([M]) to the number of the atoms of totalmetal elements contained M the crystalline oxide 21 ([A]) (=[M]/[A]) isabout 0.3 to 4.2%, the electric resistivity was about 10² Ωcm to 10³Ωcm.

The crystalline oxide indicated by the circle had an electricresistivity of about 10⁻³ Ωcm.

From the above-mentioned measurement results, as for the crystallineoxide 21, the added amount of zinc may exceed about 0.1 at %, preferablyabout 0.5 at %, and the added amount of zinc may be about 12 at % orless, preferably about 10 at % or less. The crystalline oxide 21 may bea transparent crystalline indium oxide thin film which has a bixbyitestructure of indium oxide in the crystalline structure in thecrystalline state. By using this transparent crystalline indium oxidethin film in the field-effect thin film transistor 1, a normally-offtransistor with an on-off ratio exceeding 10³ could be constituted.

In addition, by further increasing the crystallization temperature, itis possible to increase the amount of zinc oxide to be added. However,it is not industrially preferable in respect of energy required for atreatment at high temperatures.

When the sputtering apparatus 5 or the materials used in thisfilm-forming example are used, the crystallization treatment conditionsafter film formation by sputtering may be 200° C. or higher and 300° C.or lower in the air, for example. Although not shown, in the crystallineoxide 21 in this film-forming example, the electron mobilitylogarithmically proportionally increased with an increase in electroncarrier concentration. Further, it is preferable to conduct filmformation in an atmosphere containing an oxygen gas while intentionallyomitting addition of impurities ions for increasing an electricresistivity.

It is preferred that the crystalline oxide 21 of this embodiment havePAN resistance. In this way, the freedom of production process isenhanced, whereby TFT1 can be produced efficiently. In addition,reliability or the like is improved since no damage is exerted when thesource electrode 22 and the drain electrode 23 are etched with aPAN-based etching solution. In the crystalline oxide 21 of thisembodiment is subjected to patterning in an amorphous state, followed bycrystallization. Since the crystalline oxide 21 which has beencrystallized normally has PAN resistance, the source electrode 22 andthe drain electrode 23 can be subjected to patterning easily.

Here, the “having PAN resistance” means having an etching speed with aPAN-based etching solution of less than about 10 nm/min. Generally, asthe PAN-based etching solution (an etching solution containingphosphoric acid, nitric acid and acetic acid), one which containsphosphoric acid of about 45 to 95 wt %, nitric acid of about 0.5 to 5 wt% and acetic acid of about 3 to 50 wt % is used.

Further, it is preferred that the concentration of Li and Na in thecrystalline oxide 21 be 1,000 ppm or less. In this way, the propertiesdo not vary largely when driven for a long period of time, wherebyreliability of the TFT1 can be improved. The concentration of Li and Nais preferably 100 ppm or less, further preferably 10 ppm or less, with 1ppm or less being particularly preferable.

Preparation Example 1 of a Field-Effect Thin Film Transistor

Next, the preparation example of a field-effect thin film transistor 1using the above-mentioned crystalline oxide 21 will be explained withreference to the drawings.

FIG. 6 is a schematic view of essential parts for explaining the methodfor producing a field-effect thin film transistor which is asemiconductor device according to one embodiment in the second aspect ofthe invention, in which (a) is a cross-sectional view showing the statein which a gate electrode is formed, (b) is a cross-sectional viewshowing the state in which a gate-insulating film is formed, and (c) isa cross-sectional view showing the state in which a crystalline oxide isformed.

As shown in FIG. 6( a), on a glass substrate 10, indium oxide containingtin oxide (10 wt %) (ITO) was formed into a film by a sputtering methodwith a substrate temperature being at 200° C. Subsequently, aphotoresist was applied, and patterns of a gate electrode 25 and a wire(not shown) were exposed to light by using a photomask, followed bydevelopment with a developer. Subsequently, the gate electrode 25 andthe wiring pattern were formed by etching using a PAN-based etchingsolution of 35° C. (91.4 wt % of phosphoric acid, 3.3 wt % of nitricacid and 5.3 wt % of acetic acid).

Subsequently, as shown in FIG. 6( b), on the gate electrode 25, thewiring and the glass substrate 10, as a gate-insulating film 24, an SiNxfilm was formed by a sputtering method at a substrate temperature of350° C.

When the crystalline oxide 21 is used as a channel layer, as thematerial of the gate-insulating film 24, any one of Al₂O₃, SiO₂ andSiNx, or a mixed compound containing at least two of these compounds canbe given.

That is, if a fault exists in an interface between the gate-insulatingfilm 24 and the channel layer (crystalline oxide 21) thin film, theelectron mobility may be lowered or hysteresis may occur in transistorproperties. Further, current leakage largely depends on the type of thegate-insulating film 24. Therefore, it is necessary to select agate-insulating film which is suited to the channel layer. If the Al₂O₃film is used, it is possible to decrease current leakage. IF the SiO₂film is used, hysteresis can be small. Further, if an SiNx with a highdielectric constant is used, the electron mobility can be large.Further, by stacking these films, it is possible to obtain a TFTsuffering from a small degree of current leakage and hysteresis andhaving a high degree of electron mobility. In addition, since thegate-insulating film formation process and the channel layer formationprocess can be conducted at room temperature, as the TFT structure, botha bottom-gate type TFT and a top-gate type TFT can be formed.

Next, above the gate electrode 25 and on the gate-insulating film 24, anamorphous indium oxide thin film containing 5 at % of zinc was formed bya sputtering method with the substrate being at room temperature and ata sputtering pressure of 0.3 Pa. As a result, a 50 nm-thicksemi-insulating amorphous indium oxide film used as a channel layer wasformed. Subsequently, the film was etched by a photolithographic method,whereby a channel layer was formed. Thereafter, the channel layer wassubjected to a heat treatment in the air at 250° C. for one hour toallow it to be crystallized (see FIG. 6( c)).

The crystalline oxide 21 obtained by crystallization had an electriccarrier concentration of 0.6×10¹⁶/cm³, showing that the electric carrierconcentration was less than 10¹⁶/cm³.

Then, on the crystalline oxide 21 and the gate-insulating film 24, Auwas formed into a film by a mask deposition method. Subsequently, aphotoresist was applied, and patterns of a source electrode 22, a drainelectrode 23 and a wiring were exposed to light by using a photomask,followed by development with a developer. By etching using a PAN-basedetching solution of 35° C., the source electrode 22, the drain electrode23 and the wiring were formed (see FIG. 1).

ITO was used in the gate electrode 25 and the wiring thereof, and Au wasused in the source electrode 22, the drain electrode 23 and the wiringthereof. The materials are not limited thereto. For example, ZnO, SnO₂,In₂O₃, ITO, IZO, Au, Ag, Al, Cu or the like can be used. In addition,thin films formed of different materials may be stacked.

If used in a liquid display or the like where light transmittance isrequired, as the source electrode 22, the drain electrode 23 and thegate electrode 25 a transparent electrode were used. As the wiring to beconnected with these electrodes, a layer of a metal with a high electricconductivity such as Au can be used. In this case, normally, in thevicinity of the source electrode 22, the drain electrode 23 and the gateelectrode 25, it has a structure in which a transparent electrode (or awiring of a transparent electrode) and a metal layer are stacked.

When forming the crystalline oxide 21, a step of crystallizing byheating in the air is included. When an SiNx film or the like is formedas a passivasion film on the thus formed TFT, the above-mentionedcrystallization by heating may be conducted during the step of formingthe passivasion film, or may be conducted during a heating step forensuring uniformity of a TFT device on the entire substrate surface. Insuch a case, it is important to set the oxygen partial pressure higherwhen a film is formed by sputtering. As a result, generation of carriersdue to oxygen deficiency can be suppressed. As the partial oxygenpressure during film formation by sputtering, 5% or more is preferable.Although there is no upper limit, it is preferred the partial oxygenpressure be 20% or less, with 7 to 15% being more preferable.

In the film formation by the vapor phase method, by controlling thesubstrate temperature at the time of film formation, the crystallineoxide 21 with an electron carrier concentration of less than 10¹⁸/cm³can be formed at the time of film formation.

The on-off ratio of the field-effect thin film transistor 1 in thispreparation example exceeded 10³. In addition, when a field-effectmobility was calculated from output characteristics, a field-effectmobility of about 7 cm²/V·sec was obtained in the saturation region.Further, the threshold voltage (Vth) was about +0.5V, showingnormally-off properties. The output characteristics showed a clearpinch-off. The thus produced field-effect thin film transistor 1 wasirradiated with visible rays to conduct a similar measurement, and nochange in transistor characteristics was observed. That is, according tothe invention, a thin film transistor provided with a channel layerhaving a small electron carrier concentration and, therefore, having ahigh electrical resistivity and a high electron mobility can berealized.

The crystalline indium oxide thin film had excellent properties that theelectron mobility increased with an increase in electron carrierconcentration and exhibited degenerate conductance.

[Evaluation of Transistor Properties]

Next, the current-voltage characteristics of the field-effect transistor1 of this preparation example 1 will be explained with reference to thedrawings.

FIG. 7 is a current-voltage characteristics graph of a field-effect thinfilm transistor according to Preparation Example.

FIG. 7 shows the current-voltage characteristics of the field-effectthin film transistor 1 measured at room temperature. From the fact thatthe drain current I_(DS) increases with an increase in the gate voltageV_(GS), it can be understood that the channel is an n-typesemiconductor. This does not contradict the fact that a crystallineindium oxide-based semiconductor is of n-type. In addition, I_(DS)showed typical semiconductor transistor behavior that it saturated(pinch off) at around V_(DS)=10V. The gain properties were alsoexamined. As a result, it was found that the threshold value of the gatevoltage V_(GS) at the time of V_(DS)=4V was about 2.0V. When V_(DS)=10V,a current I_(DS)=1.0×10⁻⁵ A was flown. The reason therefor is thatcarriers could be induced within the crystalline indium oxidesemiconductor thin film of an insulating semiconductor by gate bias.

In this preparation example, the field-effect thin film transistor 1 wasformed on the glass substrate 10. Film formation itself could beconducted at room temperature, and crystallization could be conducted atlower temperatures by low-temperature plasma crystallization or thelike. Therefore, a substrate such as a plate or film of plastics can beused. In addition, the crystalline indium oxide thin film obtained inthis preparation example absorbs almost no visible rays, and hence, canrealize a transparent, flexible TFT.

As mentioned above, in the field-effect thin film transistor 1 of thisembodiment, since the above-mentioned crystalline oxide 21 is used asthe channel layer, it shows the following transistor characteristics.That is, it shows normally-off characteristics with a gate current ofless than 0.1 μA is flown when the transistor is in the off state and anon-off ratio exceeds 10³. In addition, it has transparency or lighttransmittance to visible rays, and also has flexibility. Further,stability, uniformity, reproducibility, heat resistance, durability orthe like of the field-effect thin film transistor 1 can be improved.Further, it is possible to provide a TFT substrate with alarge-area-uniformity or reproducibility.

Then, another preparation example of the field-effect thin filmtransistor will be explained with reference to the drawings.

Preparation Example 2 of the Field-Effect Thin Film Transistor

FIG. 8 is a schematic cross-sectional view of a top-gate typefield-effect thin film transistor which is a semiconductor deviceaccording to one embodiment in the second aspect of the invention.

In FIG. 8, a field-effect thin film transistor 1 a of this preparationexample is a top-gate thin film transistor, and is used in a TFTsubstrate or the like.

On the glass substrate 10, an IZO (registered trademark) with a largeelectroconductivity was stacked in a thickness of 40 nm by a sputteringfilm forming method. Then, a photoresist was applied, and by using aphotomask, patterns of the source electrode 22, the drain electrode 23and the wiring were exposed to light, followed by development with adeveloper. Then, by etching using a PAN-based etching solution (91.4 wt% of phosphoric acid, 3.3 wt % of nitric acid, and 5.3 wt % of aceticacid) of 45° C., the source electrode 22, the drain electrode 23 and thewiring were formed.

Next, on the glass substrate 10, an amorphous zinc oxide (8 at %)/indiumoxide (92 at %) film to be used as the channel layer was formed in athickness of 50 nm. A pattern of the active layer was exposed to lightby means of a photomask, and developed with a developer. Then, as anoxalic acid-based etching solution, etching was conducted using ITO-06N(Kanto Kagaku Kabushiki Kaisha) of 45° C. Subsequently, crystallizationwas conducted at 280° C. for one hour in air to form the crystallineoxide 21. This crystalline oxide 21 had an electron carrierconcentration of 0.7×10¹⁶/cm³, showing that it was less than 10¹⁶/cm³.

Next, on the crystalline oxide 21, the gate-insulating film 24 composedof SiO₂ was formed. Subsequently, on the gate electrode 25, IZO wasformed into a film. Then, the gate electrode 25 was formed by aphotolithographic method and etching.

The field-effect thin film transistor 1 a of this preparation examplehad the following properties. Field-effect mobility; 25 cm²/V·sec,on-off ratio; 10⁵ or more; threshold voltage (Vth); +2.0V (normally off)The output characteristics showed a clear pinch-off. That is, it hadsufficiently good transistor characteristics. Further, by using atransparent electrode, light transmittance could be improved.

Preparation Example 3 of the Field-Effect Thin Film Transistor

The field-effect thin film transistor 1 a of this preparation example isa top-gate thin film transistor as shown in FIG. 8.

At first, on the glass substrate 10, Au and IZO with a highelectroconductivity (containing 10.7 wt % of zinc oxide) wererespectively formed into a thickness of 50 nm by a sputteringfilm-forming method (Ar: 100%, total pressure: 0.3 Pa). Then, aphotoresist was applied, and by using a photomask, patterns of thesource electrode 22, the drain electrode 23 and the wiring were exposedto light, followed by development with a developer. Then, by etchingwith a PAN-based etching solution of 45° C. (91.4 wt % of phosphoricacid, 3.3 wt % of nitric acid and 5.3 wt % of acetic acid), the sourceelectrode 22, the drain electrode 23 and the wiring were formed.

Next, on the glass substrate 10, an amorphous zinc oxide (5 at %)/indiumoxide (95 at %) film to be used as the channel layer was formed in athickness of 100 nm. A pattern of the active layer was exposed to lightby means of a photomask, and developed with a developer. Then, etchingwas conducted using ITO-06N (Kanto Kagaku Kabushiki Kaisha) of 45° C. asan oxalic acid-based etching solution. Subsequently, crystallization wasconducted at 280° C. for one hour in argon gas flow containing 30 vol %of oxygen to form the crystalline oxide 21. This crystalline oxide 21had an electron carrier concentration of 0.6×10¹⁶/cm³, showing that itwas less than 10¹⁶/cm³.

Next, on the crystalline oxide 21, the gate-insulating film 24 composedof SiO₂ and SiNx was formed.

Subsequently, on the gate electrode 25, Al was formed into a film. Then,the gate electrode 25 was formed by a photolithographic method andetching.

The field-effect thin film transistor 1 a of this preparation examplehad the following properties. Field-effect mobility; 20 cm²/V·sec,on-off ratio; 10⁴ or more; threshold voltage (Vth); +1.5V (normally off)The output characteristics showed a clear pinch-off. That is, it hadsufficiently good transistor characteristics. Further, by using atransparent electrode, light transmittance could be improved.

Preparation Example 4 of the Field-Effect Thin Film Transistor

The field-effect thin film transistor 1 a of this example is a top-gatethin film transistor as shown in FIG. 8.

On the glass substrate 10, IZO having a large electric conductivity(containing 10.7 wt % of zinc oxide) was stacked into a thickness of 60nm by a sputtering film-forming method (Ar: 99%, O₂: 1%, total pressure:0.3 Pa). Then, a photoresist was applied, and by using a photomask,patterns of the source electrode 22, the drain electrode 23 and thewiring were exposed to light, followed by development with a developer.Then, by etching with a PAN-based etching solution of 45° C. (91.4 wt %of phosphoric acid, 3.3 wt % of nitric acid and 5.3 wt % of aceticacid), the source electrode 22, the drain electrode 23 and the wiringwere formed.

Next, on the glass substrate 10, an amorphous zinc oxide (5 at%)/ytterbium oxide (1 at %)/indium oxide (94 at %) film was formed asthe channel layer was stacked into a thickness of 120 nm. A pattern ofthe active layer was exposed to light by means of a photomask, anddeveloped with a developer. Then, etching was conducted using, as anoxalic acid-based etching solution, ITO-06N (Kanto Kagaku KabushikiKaisha) of 45° C.

Then, on the above-mentioned channel layer, the SiNx film was formed bythe CVD method at a substrate temperature of 320° C., thereby formingthe gate-insulating film 24. At this time, the substrate temperature waselevated to 320° C. The conductive amorphous zinc oxide (5 at%)/ytterbium oxide (1 at %)/zinc oxide ytterbium oxide (94 at %) filmwas crystallized. By the X-ray diffraction, a clear peak derived fromthe bixbyite structure of indium oxide was observed, whereby thecrystalline oxide 21 was completed. The electron carrier concentrationof the crystalline oxide 21 was 0.4×10¹⁶/cm³, showing that it was lessthan 10¹⁶/cm³.

Next, on the gate electrode 25, Al was formed into a film, and the gateelectrode 25 was formed by a photolithographic method and etching.

The field-effect thin film transistor 1 a of this preparation examplehad the following properties. Field-effect mobility; 30 cm²/V·sec,on-off ratio; 10⁶ or more; threshold voltage (Vth); +0.5V (normally off)The output characteristics showed a clear pinch-off. That is, it hadsufficiently good transistor characteristics. Further, by using atransparent electrode, light transmittance could be improved. In thefield-effect thin film transistor 1 a of this preparation example,disadvantages such as short circuits of a gate or change in current withthe passage of time could be suppressed. That is, according to theinvention, a highly reliable TFT panel which is suited to the driving ofa large-area liquid crystal panel or an organic EL panel can beprepared.

Preparation Example 5 of a Field-Effect Thin Film Transistor

The field-effect thin film transistor 1 a of this preparation example isa top-gate thin film transistor as shown in FIG. 8.

First, instead of the glass substrate 10, plastic films (for example, apolyethylene terephthalate film) were used. First, on this plastic film,a surface coat layer (for example, an amorphous silicon nitride layer:300 nm) was stacked. The materials of the surface coat layer are notlimited to amorphous silicon nitride. For example, amorphous siliconoxide, titanium oxide, aluminum oxide, magnesium oxide or the like canbe used. In this way, the adhesion with the substrate (substrate, filmor the like) was improved, and irregularities on the substrate surfacewere decreased, whereby the current leakage of the device could besuppressed.

Then, by a sputtering film-forming method (Ar: 100%, total pressure: 0.3Pa), Au and IZO (containing 10.7 wt % of zinc oxide) with a largeelectroconductivity were respectively stacked in a thickness of 30 nm.Then, a photoresist was applied, and the patterns of the sourceelectrode 22, the drain electrode 23 and the wiring were exposed tolight, followed by development with a developer. Then, by etching with aPAN-based etching solution of 45° C. (91.4 wt % of phosphoric acid, 3.3wt % of nitric acid and 5.3 wt % of acetic acid), the source electrode22, the drain electrode 23 and the wiring were formed.

Then, by a sputtering method (substrate temperature: room temperature),on the plastic film, the oxide 21 (zinc oxide (2 at %)+indium oxide (98at %)) as the channel layer was formed into a film. The pattern of anactive layer was exposed to light by using a photomask, followed bydevelopment with a developer.

Then, etching was conducted using, as an oxalic acid-based etchingsolution, ITO-06N (Kanto Kagaku Kabushiki Kaisha) of 45° C. That is, asa result of X-ray diffraction of the thin film of zinc oxide (2 at%)+indium oxide (98 at %), no peak derived from the bixbyite structureof indium oxide was observed, showing that this was an amorphous film.Subsequently, the substrate was crystallized by heating at 180° C. toobtain the crystalline oxide 21. The resulting crystalline oxide 21 hadan electron carrier concentration of 0.9×10¹⁸/cm³, showing that it wasless than 10¹⁸/cm³.

On this crystalline oxide 21, an interfacial passivasion layer(amorphous silicon oxide layer: 3 nm) was deposited, and shaped by aphotolithographic method and etching. The materials of the passivasionlayer is not limited to amorphous silicon oxide. For example, amorphoussilicon nitride, titanium oxide, aluminum oxide, magnesium oxide or thelike can be used. In this way, by forming an interfacial passivasionlayer, it effectively acts on the gate-insulating film 24, wherebycurrent leakage can be suppressed.

Instead of forming the interfacial passivasion layer, an interfacialpassivasion treatment may be conducted. That is, even when an oxygenplasma treatment (O₂: 5 sccm, 20 W, 20 sec) is conducted for theuppermost surface of the crystalline oxide 21 as the channel layer, theinterface with the gate-insulating layer can be improved, and currentleakage of the device can be suppressed. If the interfacial passivasiontreatment is formed and the interfacial passivation layer is formed,current leakage of the device can more effectively suppressed.

Next, on the crystalline oxide 21, the gate-insulating film 24 composedof SiO₂ was formed. Subsequently, Al was formed into a film on the gateelectrode 25. Then, the gate electrode 25 was formed by aphotolithographic method and etching.

The field-effect thin film transistor 1 a of this preparation examplehad the following properties. Field-effect mobility; 25 cm²/V·sec,on-off ratio; 10⁵ or more; threshold voltage (Vth); +0.5V (normally off)The output characteristics showed a clear pinch-off. That is, it hadsufficiently good transistor characteristics. Further, by using atransparent electrode, light transmittance could be improved.

Hereinabove, the semiconductor device of the second aspect of theinvention was explained with reference to preferable embodiments. Thesemiconductor device according to the second aspect of the invention isnot limited to the above-mentioned embodiments. It is needless to saythat various modifications are possible within the scope of theinvention.

For example, the field-effect thin film transistor is not limited to abottom-gate or top-gate field-effect thin film transistor. Field-effecttransistors varying in structure may be used.

EXAMPLES

The first aspect of the invention will be explained with reference tothe examples, while comparing with the comparative examples. Theexamples only show preferable examples, and the invention is notrestricted to the examples. Therefore, modifications based on thetechnical idea of the first aspect of the invention, and other examplesthereof are included in the first aspect of the invention.

The method for measuring the properties of a sputtering target preparedin Examples and Comparative Examples are given below.

(1) Density

Calculated from the weight and the external dimension of a piece of atarget which had been cut into a predetermined size.

(2) Bulk Resistance of a Target

Measured by the four probe method by using a resistivity meter (Loresta,manufactured by Mitsubishi Chemical Corporation).

(3) Structure of an Oxide Present in a Target

The structure of an oxide was identified by analyzing the chart obtainedby the X-ray diffraction.

Example 1

950 g of indium oxide and 50 g of gadolinium oxide (raw material powder)were pulverized with mixing for about 5 hours by using a dry beads mill,whereby mixed powder was prepared.

The resulting mixed powder was put in a mold with a dimension with adiameter of 10 mm. After conducting preliminary molding at a pressure of100 kg/cm² by means of a mold pressing machine, the resultant wascompacted to a molded product at a pressure of 4 t/cm² by means of acold isostatic pressing machine.

The molded product was fired at 1250° C. for 15 hours, whereby asintered body was produced.

For the resulting sintered body, an X-ray diffraction measurement wasconducted. As a result, only an X-ray diffraction peak derived fromIn₂O₃ was observed, confirming that the resulting sintered body wassubstantially of a bixbyite structure. The X-ray diffraction chart ofthis sintered body is shown in FIG. 9.

The atomic ratio of this sintered body was measured by ICP (InductivityCoupled Plasma) analysis, and it was found that Gd/(Gd+In)=4 at %.Further, the in-plane elemental distribution was evaluated by EPMA(Electron Probe Micro Analyzer). As a result, the dispersed state of Inand Gd was confirmed. The composition thereof was substantially uniform.

The sintered body had a density of 6.95 g/cm³ and a bulk resistance of0.05 Ωcm.

Example 2

A sintered body was produced in the same manner as in Example 1, exceptthat 900 g of indium oxide and 100 g of dysprosium oxide were used asthe raw material powder.

An X-ray diffraction measurement was conducted for the resultingsintered body. As a result, only a diffraction peak derived from In₂O₃was observed, confirming that the resulting sintered body wassubstantially of a bixbyite structure. The X-ray diffraction chart ofthis sintered body is shown in FIG. 10.

The atomic ratio of this sintered body was measured by ICP analysis, andit was found that Dy/(Dy+In)=7.6 at %. Further, the in-plane elementaldistribution was evaluated by EPMA. As a result, the dispersed state ofIn and Dy was confirmed. The composition thereof was substantiallyuniform.

The sintered body had a density of 6.98 g/cm³ and a bulk resistance of0.004 Ωcm.

Example 3

A sintered body was produced in the same manner as in Example 1, exceptthat 950 g of indium oxide and 50 g of holmium oxide were used as theraw material powder.

An X-ray diffraction measurement was conducted for the resultingsintered body. As a result, only a diffraction peak derived from In₂O₃was observed, confirming that the resulting sintered body wassubstantially of a bixbyite structure. The X-ray diffraction chart ofthis sintered body is shown in FIG. 11.

The atomic ratio of this sintered body was measured by ICP analysis, andit was found that Ho/(Ho+In)=3.7 at %. Further, the in-plane elementaldistribution was evaluated by EPMA. As a result, the dispersed states ofIn and Ho were confirmed. The composition thereof was substantiallyuniform.

The sintered body had a density of 6.76 g/cm³ and a bulk resistance of0.004 Ωcm.

Example 4

A sintered body was produced in the same manner as in Example 1, exceptthat 900 g of indium oxide and 100 g of erdium oxide were used as theraw material powder.

An X-ray diffraction measurement was conducted for the resultingsintered body. As a result, only a diffraction peak derived from In₂O₃was observed, confirming that the resulting sintered body wassubstantially of a bixbyite structure. The X-ray diffraction chart ofthis sintered body is shown in FIG. 12.

The atomic ratio of this sintered body was measured by ICP analysis, andit was found that Er/(Er+In)=7.5 at %. Further, the in-plane elementaldistribution was evaluated by EPMA. As a result, the dispersed states ofIn and Er were confirmed. The composition thereof was substantiallyuniform.

The sintered body had a density of 6.86 g/cm³ and a bulk resistance of0.005 Ωcm.

Example 5

A sintered body was produced in the same manner as in Example 1, exceptthat 900 g of indium oxide and 100 g of ytterbium oxide were used as theraw material powder.

An X-ray diffraction measurement was conducted for the resultingsintered body. As a result, only a diffraction peak derived from In₂O₃was observed, confirming that the resulting sintered body wassubstantially of a bixbyite structure. The X-ray diffraction chart ofthis sintered body is shown in FIG. 13.

The atomic ratio of this sintered body was measured by ICP analysis, andit was found that Yb/(Yb+In)=7.3 at %. Further, the in-plane elementaldistribution was evaluated by EPMA. As a result, the dispersed states ofIn and Yb were confirmed. The composition thereof was substantiallyuniform.

The sintered body had a density of 6.91 g/cm³ and a bulk resistance of0.004 Ωcm.

Example 6

A sintered body was produced in the same manner as in Example 1, exceptthat 890 g of indium oxide, 100 g of ytterbium oxide and 10 g of zincoxide were used as the raw material powder.

An X-ray diffraction measurement was conducted for the resultingsintered body. As a result, only a diffraction peak derived from In₂O₃was observed, confirming that the resulting sintered body wassubstantially of a bixbyite structure. The atomic ratio of this sinteredbody was measured by ICP analysis, and it was found that Yb/(Yb+In)=7.2at % and Zn/(Yb+In +Zn)=1.6 at %. Further, the in-plane elementaldistribution was evaluated by EPMA. As a result, the dispersed states ofIn, Yb and Zn were confirmed. The composition thereof was substantiallyuniform.

The sintered body had a density of 6.84 g/cm³ and a bulk resistance of0.003 Ωcm.

Example 7

A sintered body was produced in the same manner as in Example 1, exceptthat 949 g of indium oxide, 50 g of gadolinium oxide and 1 g of ceriumoxide were used as the raw material powder.

An X-ray diffraction measurement was conducted for the resultingsintered body. As a result, only a diffraction peak derived from In₂O₃was observed, confirming that the resulting sintered body wassubstantially of a bixbyite structure. The atomic ratio of this sinteredbody was measured by ICP analysis, and it was found that Gd/(Gd+In)=4 at%. The content of Ce relative to the total metal elements was 800 ppm.Further, the in-plane elemental distribution was evaluated by EPMA. As aresult, the dispersed state of In and Gd was confirmed. The compositionthereof was substantially uniform.

The sintered body had a density of 6.95 g/cm³ and a bulk resistance of0.001 Ωcm.

Examples 8 to 11

Sintered bodies were produced in the same manner as in Example 7, exceptthat Ge, Ti, Zr and Nb were used instead of Ce. The resulting sinteredbodies each had a bulk resistance of 0.005 Ωcm or less, showing thatthey were sintered bodies capable of being subjected to a DC magnetronsputtering method.

Example 12

A sintered body was produced in the same manner as in Example 1, exceptthat 949 g of indium oxide, 50 g of gadolinium oxide and 1 g of tinoxide were used as the raw material powder.

An X-ray diffraction measurement was conducted for the resultingsintered body. As a result, only a diffraction peak derived from In₂O₃was observed, confirming that the resulting sintered body wassubstantially of a bixbyite structure. The atomic ratio of this sinteredbody was measured by ICP analysis, and it was found that Gd/(Gd+In)=4 at%. The content of Sn relative to the total metal elements was 900 ppm.Further, the in-plane elemental distribution was evaluated by EPMA. As aresult, the dispersed state of In and Gd was confirmed. The compositionthereof was substantially uniform.

The sintered body had a density of 6.94 g/cm³ and a bulk resistance of0.05 Ωcm.

Comparative Example 1

A sintered body was produced in the same manner as in Example 1, exceptthat 600 g of indium oxide and 400 g of gadolinium oxide were used asthe raw material powder.

As a result of an X-ray diffraction measurement, not only an X-raydiffraction peak derived from In₂O₃ but also a peak derived from GdInO₃was observed. An X-ray diffraction chart is shown in FIG. 14.

The atomic ratio of this sintered body was measured by ICP analysis, andit was found that Gd/(Gd+In)=34 at %. Further, the in-plane elementaldistribution was evaluated by EPMA. As a result, the dispersed state ofIn and Gd was confirmed. Gd was un-uniformly dispersed.

The sintered body had a density of 6.46 g/cm³ and a bulk resistance of1.5 Ωcm.

Example 13

The sintered body of Example 1 was processed to obtain a sputteringtarget with a diameter of 4 inches. This sputtering target was bonded toa backing plate, and then installed in a DC sputtering apparatus. In anargon gas atmosphere having an oxygen concentration of 1%, a 50 nm-thickthin film was formed at 100 W (1 W/cm²) with the substrate temperaturebeing room temperature.

The bulk resistance of this thin film was 0.008 Ωcm, which showed thatthis film was a thin film having a good conductivity.

An X-ray diffraction analysis was conducted for this thin film. No peakwas observed, confirming that this thin film was of a good amorphousstructure.

The atomic ratio of this thin film was measured by an ICP analysis, andwas found to be Gd/(Gd+In)=4 at %.

This amorphous thin film was subjected to a heating treatment in the airat 240° C. for one hour. The bulk resistance of this heat-treated thinfilm was 4 Ωcm, confirming that this is a semiconductor film.

An X-ray diffraction analysis was conducted for the resulting oxidesemiconductor film. As a result, only an X-ray diffraction peak derivedfrom In₂O₃ was observed, confirming that the resulting oxidesemiconductor thin film was substantially of a bixbyite structure.

Examples 14 to 17

Thin films were formed in the same manner as in Example 13, except thatthe sintered bodies produced in Examples 2 to 5 were used instead of thesintered body produced in Example 1.

Each of the resulting thin films was amorphous. In the same manner as inExample 13, each of the resulting amorphous thin films was subjected toa heating treatment. It was confirmed that the thin films which had beensubjected to a heat treatment were a semiconductor film.

An X-ray diffraction measurement was conducted for each of the resultingoxide semiconductor films. As a result, only an X-ray diffraction peakderived from In₂O₃ was observed, confirming that the resulting oxidesemiconductor films were substantially of a bixbyite structure.

Example 18

A thin film was formed in the same manner as in Example 13, except thatthe sintered body produced in Example 7 was used instead of the sinteredbody produced in Example 1.

The bulk resistance of this thin film was 0.0009 Ωcm, which showed thatthis film was a thin film having a good conductivity. An X-raydiffraction measurement was conducted for this thin film. Since no peakwas observed, it was confirmed that this film was of a good amorphousstructure.

The atomic ratio of this sintered body was measured by ICP analysis, andit was found that Gd/(Gd+In)=4 at %. The content of Ce relative to thetotal metal elements was 800 ppm.

The resulting amorphous thin film was subjected to a heat treatment inthe same manner as in Example 13. The bulk resistance of theheat-treated thin film was 8 Ωcm, confirming that this thin film was asemiconductor film.

An X-ray diffraction measurement was conducted for this thin film. As aresult, only an X-ray diffraction peak derived from In₂O₃ was observed,confirming that the resulting oxide semiconductor film was substantiallyof a bixbyite structure.

Examples 19 to 22

Thin films were formed in the same manner as in Example 13, except thatthe sintered bodies produced in Examples 8 to 11 were used instead of asintered body produced in Example 1.

Each of the resulting thin films was amorphous. Each of the resultingamorphous thin films was subjected to a heat treatment in the samemanner as in Example 13. It was confirmed that each of the thin filmswhich were subjected to a heat treatment was a semiconductor film.

An X-ray diffraction measurement was conducted for this thin film. As aresult, only an X-ray diffraction peak derived from In₂O₃ was observed,confirming that the resulting oxide semiconductor film was substantiallyof a bixbyite structure.

Example 23

A thin film was formed in the same manner as in Example 13, except thatthe sintered body produced in Example 6 was used instead of the sinteredbody produced in Example 1.

The bulk resistance of this thin film was 0.0006 Ωcm, which showed thatthis film was a thin film having a good conductivity. An X-raydiffraction measurement was conducted for this thin film. Since no peakwas observed, it was confirmed that these films were of a good amorphousstructure.

The atomic ratio of this sintered body was measured by ICP analysis, andit was found that Yb/(Yb+In +Zn)=7.0 at %, and Zn/(Yb+In +Zn)=1.5 at %.

The resulting amorphous thin film was subjected to a heat treatment inthe same manner as in Example 13. The bulk resistance of theheat-treated thin film was 100 Ωcm, confirming that this thin film was asemiconductor film.

An X-ray diffraction measurement was conducted for this thin film. As aresult, only an X-ray diffraction peak derived from In₂O₃ was observed,confirming that the resulting oxide semiconductor film was substantiallyof a bixbyite structure.

INDUSTRIAL APPLICABILITY

The sputtering target according to the first aspect of the invention issuitable as a raw material of an oxide semiconductor film such as aswitching element, a driving circuit element, etc. of a liquid displayapparatus, a thin film electroluminescence display apparatus, anelectrophoresis display, a moving powder display or the like. Forexample, an oxide semiconductor film for driving a liquid display and anoxide semiconductor film for driving an organic EL device can beobtained.

The semiconductor device using the crystalline oxide according to thesecond aspect of the invention can be widely used in varioussemiconductor devices, semiconductor apparatuses, circuits or the like.For examples, it can be widely applied to a flexible display such as aplastic film using a flexible material, an IC card, an ID tag or thelike. A transistor using the transparent crystalline oxide filmaccording to the second aspect of the invention is suitable as aswitching element of a large-sized LCD or an organic EL display.

1-12. (canceled)
 13. A semiconductor device using a crystalline oxidecomprising indium as a semiconductor, wherein the crystalline oxide hasan electron career concentration of less than 10¹⁸/cm³.
 14. Thesemiconductor device according to claim 13, wherein the crystallineoxide is a nondegenerate semiconductor.
 15. The semiconductor deviceaccording to claim 13, wherein the crystalline oxide comprises apositive divalent element.
 16. The semiconductor device according toclaim 15, wherein the positive divalent element is at least one elementof Zn, Mg, Ni, Co and Cu.
 17. The semiconductor device according toclaim 15, wherein the atomic ratio of the number of the atoms of thepositive divalent element ([M2]) to the number of the atoms of totalmetal elements contained in the crystalline oxide ([A]) is0.001≦[M2]/[A]<0.2.
 18. The semiconductor device according to claim 17,wherein the electron mobility to the electron carrier concentration ofthe crystalline oxide logarithmically proportionally increases by atleast changing the atomic ratio of [M2] to [A].
 19. The semiconductordevice according to claim 13, wherein the crystalline oxide comprises apositive trivalent element other than indium.
 20. The semiconductordevice according to claim 19, wherein the positive trivalent element isat least one element of B, Al, Ga, Sc, Y and a lanthanoid element. 21.The semiconductor device according to claim 19, wherein the atomic ratioof the number of the atoms of the positive trivalent element ([M3]) tothe number of the atoms of total metal elements contained in thecrystalline oxide ([A]) is 0.001≦[M3]/[A]<0.2.
 22. The semiconductordevice according to claim 21, wherein the electron mobility to theelectron carrier concentration of the crystalline oxide logarithmicallyproportionally increases by at least changing the atomic ratio of [M3]to [A].
 23. The semiconductor device according to claim 13, wherein thecrystalline oxide has a PAN resistance.
 24. The semiconductor deviceaccording to claim 13, wherein the concentration of Li and Na containedin the crystalline oxide is 1000 ppm or less.
 25. The semiconductordevice according to claim 13, wherein the crystalline oxide is used as achannel layer in a field-effect transistor.
 26. The semiconductor deviceaccording to claim 13, wherein the semiconductor is obtained bysubjecting a sputtering target to sputtering, wherein said sputteringtarget is formed of an oxide sintered body comprising indium (In) and atleast one element selected from gadolinium (Gd), dysprosium (Dy),holmium (Ho), erbium (Er) and ytterbium (Yb), and the oxide sinteredbody is substantially of a bixbyite structure.
 27. The semiconductordevice according to claim 26, wherein said oxide sintered body has anatomic ratio represented by M/(In+M) of 0.01 to 0.25, wherein M is thecontent of gadolinium (Gd), dysprosium (Dy), holmium (Ho), erbium (Er)and ytterbium (Yb).
 28. The semiconductor device according to claim 26,wherein the sputtering target further comprises a positive divalentmetal element and the content of the positive divalent metal element tothe total amount of metal elements contained in the sputtering target is1 to 10 at %.
 29. The semiconductor device according to claim 28,wherein the positive divalent metal element is zinc (Zn) and/ormagnesium (Mg).
 30. The semiconductor device according to claim 26,wherein the sputtering target further comprises a metal element with anatomic valency of positive tetravalency or higher, wherein the contentof the metal element with an atomic valency of positive tetravalency orhigher to the total metal elements contained in the sputtering target is100 ppm to 2000 ppm in atomic ratio.
 31. The semiconductor deviceaccording to claim 30, wherein the metal element with an atomic valencyof positive tetravalency or higher metal element is at least one elementselected from germanium (Ge), titanium (Ti), zirconium (Zr), niobium(Nb) and cerium (Ce).